C Language Notes

ACS 168

Structured Problem Solving Using the Computer by Lynne Koenecke

In tro d u c t i o n t o M i c ro c om p ute r s

Components of a Computer Hardware components of a Computer

Central Processing Unit

Input

Output

Main Memory (Primary Storage)

RAM

Secondary Storage

Input Keyboard, Scanner, Mouse, Light Pen, Digitizing Tablet Output Monitor, Laser Printer, Dot-matrix Printer, Ink Jet Printer, Plotter, Sound Secondary Storage Floppy Disk, CD-ROM, Hard Disk, Magnetic Tape Central Processing Unit (CPU) Performs the Actual processing of information stored in memory. The part of a computer that controls all the other parts. The CPU fetches instructions from memory and decodes them. Main Memory Random Access Memory - volatile memory that holds instructions to be processed by the CPU and data ready to be used. All types of information are stored in main memory. • Data and instructions are stored sequentially. • Each memory cell has a unique address associated with it. • The information stored in a memory location is called its contents. • Every memory cell always contains some information. Address

Lynne Koenecke Illinois State University, ACS

Contents

0

-27.2

1

354

2

0.005

3

-785

4

H

.

.

.

.

98

OH

99

65.78

3

Software

System Software - controls the execution of other programs interacting with the computer. Examples: • command line interpreter • window system • assemblers • compilers • linkers • interpreters

Application Software - complete program that performs a specific function or functions for a user.

Examples of Packaged (off the shelf) Software: •Microsoft Word •Lotus 123 •Adobe Photoshop •Quicken •CAD •Eudora •Netscape Application software is also custom written for the user. In this class you will be writing customized software application programs in C. Software includes both source code written by humans and executable machine code produced by assemblers or compilers.

Lynne Koenecke Illinois State University, ACS

4

P ro g r amm in g L a n g u a g e s Machine Language The "native tongue" of a particular kind of computer. Written in binary numbers (0s and 1s). 0010 0000 0000 0100 0100 0000 0000 0101 0011 0000 0000 0110 Assembly Language Uses descriptive names to reference data. LOAD value ADD delta STORE value The result of assembly instructions is Machine Language. High-Level Language • Easier to understand • Portable - can be used on many different types of computers with few modifications. • Allow programmers to write instructions with statements that resemble English. Examples of High Level Programming Languages BASIC, COBOL, Fortran, C, Ada, Lisp, PL/I High level programs are coded into machine language by compilers. The programming statements (called source code) are checked and processed by a compiler and then coded into 0s and 1s.

Lynne Koenecke Illinois State University, ACS

5

P ro c e s s in g a H i g h -L e v e l L a n g u a g e P ro g r am Programmer enters high-level programming statements into and editor and saves it as a source file.

Source file on disk

Revised Source File

Compiler attempts to translate the program

Programmer corrects syntax errors Failure

Success

List of errors

New Object File

Other Object Files

Linker links the new object file ith other object files

Load file

Loader places the load file into memory Executable program in memory Lynne Koenecke Illinois State University, ACS

6

Source Code Editor

Preprocessed Source Code

Preprocessor

Object Code

Compiler

Executable Code Linker

External Items

E r ro r s i n P ro g r amm in g Programs rarely run correctly the first time they are compiled. Programming errors are known as “bugs”. The process of correcting errors in programs is called debugging a program.

Types of Errors Syntax Errors They are also called compilation errors. Syntax errors are detected by the compiler as it tries to translate the program statement. Syntax errors are the result of incorrect usage of the programming language's rules of syntax. Run-time Errors Run-time errors are detected by the computer as a program is executing. These errors stop the execution of the program and an error message is displayed. Logic Errors Logic errors become evident in programs that are syntactically correct and do not have run-time errors, yet the program produces an incorrect answer. It is very important that you test your program with hand calculated answers to be sure that your program works as intended.

Lynne Koenecke Illinois State University, ACS

7

H o w P ro g r am s R e c e i v e In p u t Interactive and Batch Input As programs execute, they usually receive some kind of input data to process. The program can receive data in two modes, interactive and batch.

Interactive mode - the user interacts with the program by using an input device to enter data into the computer while the program is running. Programs designed for interactive mode display messages called prompts on the screen to tell the user what data is needed at a particular point in the program.

Batch mode - all of the data provided to the program is gathered in advance. The user does not interact with a program written for batch mode. A data file is prepared before the program is executed.

D a t a vs . In f o rm a t i o n

Data - raw facts given to a computer during the input operation which is used to process information.

Information - Data that has been processed into a form that has meaning and is useful.

3 pieces of data 90 70 80

Lynne Koenecke Illinois State University, ACS

Average: 80

8

Wh a t C omp ute r s C a n D o

Five basic computer operations Computers can: 1. Receive data 

from an input device (keyboard, mouse, etc.)



from a file

2. Display/write information 

to the display device (monitor)



to a printer

3. Perform arithmetic addition, subtraction, multiplication, division 4. Compare two pieces of data and select one of two actions 5 > 6 is False

10 = 10 is True

A < B is True

5. Repeat a group of actions

Lynne Koenecke Illinois State University, ACS

9

P ro b l em S o lv i n g a n d S o ft w a re D ev e l o pm e nt Top-Down Design Most programming problems are too complex to solve all at once. Turning a problem into a program requires a programmer to create smaller problems that fit together to solve the large, complex problem. This is referred to as top-down design, because the design process starts at the top, with the main ideas, and works down to the details. The result of top-down design is an algorithm - a set of step-by-step instructions that solves the original problem.

Characteristics of Algorithms

Algorithms must . . . 1. be precise and unambiguous 2. be the correct solution in all cases 3. eventually end

Pseudocode Programmers typically write algorithms in a form called pseudocode. Pseudocode is a cross between a computer language and plain English. The pseudocode is translated into a computer language after the algorithm has been tested for correctness.

Characteristics of Pseudocode • Statements written in simple English •

Each instruction written on a separate line

•

Keywords and indentation are used to signify control

Lynne Koenecke Illinois State University, ACS

10

St e p s t o S o lv i n g a P ro b l em

Design 1. Defining the problem 2. Outline the solution 3. Develop the outline into an algorithm 4. Test the algorithm for correctness

Implementation 5. Code the algorithm into a specific programming language 6. Run the program on the computer

Design

Lynne Koenecke Illinois State University, ACS

& Co 7. De de Do bug M cu ain m tai en n t 6.

5.

1.

2. IPO 3. Stru 4. Alg ctu De or re sk ithm Ch art Ch ec k

7. Document and maintain the program

Implementation

11

1. Defining the Problem: Divide the problem into three components: inputs, processing, and outputs. We use an IPO chart to illustrate this step. I

P

O

1. List the inputs 

data items that are entered into the program from the keyboard or a file



nouns



examples: name, number, test_score, price, score

2. List the outputs 

information that has been processed by the program and/or will be output by the program



nouns



examples: total, sum, balance, average (outputs are sometimes the same as inputs)

3. List the processing steps 

steps needed during execution to solve the problem



verbs (actions)



examples: Read data, Calculate total, Determine rate, Accumulate total revenue, Print heading, Print detail

Lynne Koenecke Illinois State University, ACS

12

Example 1

Outline a solution for a program that will read 3 numbers and print the average.

I

P

number1

get numbers

number2

add numbers

number3

calculate average

O average

print average

Example 2

Outline a solution for a program that will read 3 numbers and print the numbers and the average.

I

P

O

number1

get numbers

number1

number2

add numbers

number2

number3

calculate average

number3

print average

average

Lynne Koenecke Illinois State University, ACS

13

3. Converting the IPO into an Algorithm Example 1

Average 3 numbers get number1 get number2 get number3 total = number1 + number2 + number3 average = number1 + number2 + number3/3 print “Average: “ average End Average 3 numbers 4. Desk Checking the Algorithm for Correctness 1. Choose appropriate test data. 2. Choose simple test data. 3. Check all cases. Test Data:

5, 10, 15

number1

number2

5

10

Predicted Output: 10 number3

Output

15

20

Oops! We need to revise our algorithm. The following line should have read: average = (number1 + number2 + number3)/3 or better yet: average = total / 3

Lynne Koenecke Illinois State University, ACS

14

P ro g r am C o n t ro l S tr u c tu re s Sequence Selection Repetition

Sequence Execution of one processing step after another in order. Task A Task B Task C

Selection - if . . . then . . . else Evaluation of a condition to true or false to determine a path of action. True

Print “Yes”

Is 1>2?

False

Print “No”

if 1 is greater than 2 then Print “Yes” else Print “No”

Lynne Koenecke Illinois State University, ACS

15

Repetition (looping) Repeating a group of instructions as long as a condition is true or until a condition is false.

False

? True

Pre-test loop

DO WHILE condition statement statement statement END WHILE The statements in the DO WHILE structure repeat as long as the condition is true.

Post-test loop

Counter-controlled loop

DO

DO loop_index = initial-value to final_value

statement

statement

statement

statement

statement

statement

UNTIL condition

END DO

The statements in the DO structure repeat as long as the condition is false.

Used when a loop must execute a specified number of times.

Lynne Koenecke Illinois State University, ACS

16

A c t i o n D i a g r am s Action Diagrams add an additional visual element to algorithms to indicate sequence, selection, and repetition. (Refer to the Action Diagrams section in the Appendix of your Lab Manual).

Sequence Indicates start of algorithm

Algorithm Name statement statement statement statement

Indicates end of algorithm

End Algorithm Name

Statements are followed in order from the start of the algorithm to the end of the algorithm.

Selection (IF . . . THEN) Indicates start of algorithm

Algorithm Name statement IF condition THEN statement if condition is true ELSE statement if condition is false END IF

Indicates end of algorithm

End Algorithm Name

As the statements in the algorithm are executed, a choice is made by evaluating the condition of the IF .. . THEN control structure. The dividing line indicates that only one of the statements executes based on the TRUE or FALSE evaluation of the condition.

Lynne Koenecke Illinois State University, ACS

17

Selection (CASE structure) Indicates start of algorithm

Algorithm Name statement CASE of final_grade 90 - 100: letter_grade = ‘A’ 80 - 89: letter_grade = ‘B’ 70 - 79: letter_grade = ‘C’ 60 - 69: letter_grade = ‘D’ other: letter_grade = ‘F’ END CASE

Indicates end of algorithm

End Algorithm Name

As the statements in the algorithm are executed, a choice is made by evaluating the value of final_grade and using a CASE control structure. Only one assignment is made based on the evaluation of final_grade..

Repetition Indicates start of algorithm

Algorithm Name statement DO WHILE condition statement statement statement END WHILE

Indicates end of algorithm

End Algorithm Name

As the statements in the algorithm are executed, a group of statements are repeated withing the DO WHILE control structure until the condition is evaluated to FALSE. The double line indicates repetition.

Lynne Koenecke Illinois State University, ACS

18

Va r i a b l e s As mentioned earlier, computers use main memory (RAM) to hold instructions and data for processing. High-level programs allow programmers to assign a name to a memory cell. When program statements are written, the memory cell is referred to as the name the programmer gave it. Variable Memory Locations  Temporarily hold a value  Can only hold one value at a time  If a new value is placed in a memory loation, the old one is gone forever  Values are placed in locations by assignment statements  Counters and accumulators must be initially assigned a value of zero Assignment Statement: value1 = number + variable1 Original Values Address

Name

After Assignment Statement Contents

Address

Name

Contents

0

number

10

0

number

10

1

value1

20

1

value1

15

2

variable1

5

2

variable1

5

3

sum

0

3

sum

0

4

count

0

4

count

0

.

.

.

.

.

.

.

.

98

OH

98

OH

99

65.78

99

65.78

Lynne Koenecke Illinois State University, ACS

19

C on t ro l St r u c tu re E x amp l e s Predict what the output would be for each of the following Selection Control Structures:

Example 1: num1 = 10

Output

num2 = 20 IF num1 < num2 THEN Print “num1 is less than num2” ELSE Print “num2 is less than num1” ENDIF

Example 2: variable1 = 100

Output

variable2 = 101 IF variable1 > variable2 THEN Print “variable1 is greater than variable2” ELSE Print “variable 2 is greater than variable1” ENDIF

Lynne Koenecke Illinois State University, ACS

20

Predict the output of the following Repetition Control Structures: value = 1

Output

DO WHILE value < 3 Print value value = value + 1 END WHILE Print “The last number is” value

value = 4

Output

DO WHILE value < 6 Print value value = value + 1 END WHILE Print “The Last number is” value

value = 4

Output

DO WHILE value > 0 Print value value = value - 1 END WHILE

Lynne Koenecke Illinois State University, ACS

21

Jessica A g e n t l e r In t ro d u c t i o n to P ro g r amm in g Why use Jessica? Jessica is an application program written for introductory programmers that allows practice with logic and program flow using a simple language who’s syntax can be learned quickly. Please read the section about Jessica in the back of your lab manual for the specifics about Jessica and the Jessica language. Jessica’s World • Jessica lives on Santong Island • Jessica’s home position is in the extreme Northwest corner • Jessica cannot swim • She knows direction: North, South, East, and West • She moves by hopping one space at a time • She picks flowers (*) • She gets killed by nets (#) • She can detect nets one space ahead, on her left, and on her right • She can disable a net by tossing a flower on it

Lynne Koenecke Illinois State University, ACS

22

Jessica’s Island

.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . # . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .#. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . # . . . . . . . . . ##### . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .#. . . . . . . . . . . . . . * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Lynne Koenecke Illinois State University, ACS

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C o n d it i o n s Jessica can make decisions that affect selection and repetition control structures. These decisions are based on simple conditions and NOT simple conditions. The exact phrase listed below is placed in parentheses as the condition to check for true or false. Simple Conditions

NOT Simple Conditions

AT_FLOWER

NOT AT_FLOWER

OUT_OF_FLOWERS

NOT OUT_OF_FLOWERS

NET_AHEAD

NOT NET_AHEAD

NET_ON_LEFT

NOT NET_ON_LEFT

NET_ON_RIGHT

NOT NET_ON_RIGHT

WATER_AHEAD

NOT WATER_AHEAD

FACING_NORTH

NOT FACING_NORTH

FACING_SOUTH

NOT FACING_SOUTH

FACING_EAST

NOT FACING_EAST

FACING_WEST

NOT FACING_WEST

(see p. 6 of the Jessica section of your lab manual for an explanation of each of these conditions)

Lynne Koenecke Illinois State University, ACS

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S e l e c t i o n C o n tro l S tr u c tu re s IF (condition) THEN instruction block END IF;

IF (condition) THEN instruction block ELSE instruction block END IF;

R e p e t it i o n C o n tro l S tr u c tu re s WHILE (condition) instruction block END WHILE; Legal, but not acceptable! Do (number) TIMES instruction block END DO;

This code does not always work correctly in this environment. *Notice that there are no semicolons after the IF line, ELSE line, and WHILE line. There would be appropriate semicolons after each instruction block line.

Lynne Koenecke Illinois State University, ACS

25

IP O C h a r t fo r J e s s i c a Jessica does not have any variables. Therefore, there are no inputs and no outputs. I

P

O

turn to face north hop to north beach turn left hop to west beach go to home position

Lynne Koenecke Illinois State University, ACS

26

P re - c on d i t i o n s a n d P o st-c o n d it i o n s By looking at individual statements or a group of statements in a control structure, a program can be tested for accuracy. Test data must be selected carefully to determine if the statements (or group of statements) work in all cases. (Refer to the section “Program Verification-Using Preconditions and Postconditions” in the Appendix of your lab manual.)

Pre-condition: -what is true or known before the statement (or group of statements) is executed Post-condition: -what is true or known after the statement (or group of statements) is executed

Example

number = 100 Pre-condition: number has no assigned value Post-condition: number has been assigned the value 100

Example

read balance IF balance > 200 balance = balance * 1.05 ELSE balance = balance - 5 Pre-condition: balance has a value (We don’t know the specific value. It is dependent on what is read in.)

Post-condition: Either balance has been increased by 5% or $5 has been subtracted from balance

Lynne Koenecke Illinois State University, ACS

27

Example

LEFT; Pre-condition: Jessica is in her home position at the NW corner of the island facing east. Post-condition: Jessica is facing North.

Example

Jessica is in her home position and there is no net immediately in front of her. WHILE (NOT NET_AHEAD) HOP; END WHILE; Pre-condition: Jessica is in her home position at the NW corner of the island facing east and there is no net immediately in front of her. Post-condition: Jessica is facing East. Jessica has hopped at least one space to the East. She may have hopped more than one space. There is a net in the next space to the east.

Exercises:

Indicate whether the following statements are true or false given the preconditions and postconditions as stated. If it is false, indicate why it is false. Precondition: var1 is an even integer Statement:

var1 = var1 + 1

Postcondition: var1 is an odd integer Precondition:

number is a positive integer

Lynne Koenecke Illinois State University, ACS

28

Statement: DOWHILE (number is positive) number = number - 1 ENDDO Postcondition:

number is a negative integer

Precondition:

X < Y, X and Y are positive integers

Statement:

IF X = Y THEN X=X-Y ELSE Y=Y+X ENDIF

Postcondition:

X>Y

Preconditions: Jessica is facing North. There is a net an undetermined number of spaces ahead of her. Statement:

WHILE (NOT NET_AHEAD) HOP; END WHILE;

Postcondition:

NET_AHEAD is true; Jessica is facing North

Lynne Koenecke Illinois State University, ACS

29

Members of Big R Video’s VIP Rental Club receive a 20% discount on rentals. Regular rental rates are $2 per night. Algorithm with Action Diagram: Determine Rental Rate Get member_status Get num_movies IF member_status = ‘y’ THEN rate = 2*.8 ELSE rate = 2 END IF cost = rate * num_movies Display rate End Determine

Test Cases: Member Status

Num Movies

Output

y

2

3.60

n

3

6.00

Lynne Koenecke Illinois State University, ACS

30

N e ste d I F C o n t ro l St r u c tu re s Example

Determine a student’s final grade based on a 90,80,70,60 scale. IF grade > = 90 THEN letter_grade = ‘A’ ELSE IF grade > = 80 THEN letter_grade = ‘B’ ELSE IF grade > = 70 THEN letter_grade = ‘C’ ELSE IF grade > = 60 THEN letter_grade = ‘D’ ELSE letter_grade = ‘F’ END IF END IF END IF END IF

Lynne Koenecke Illinois State University, ACS

31

Trace the following algorithm and answer the question below. num = 0 DO index = 1 to 4 num = num + index + 3 Print index, number ENDDO

Number

Index

Output

Trace the following algorithm and answer the question below. num = 0 DO index = 1 to 4 num = num + index + 3 ENDDO Print index, number Number

Lynne Koenecke Illinois State University, ACS

Index

Output

32

Design

5. 6. Co 7. De de D b M ocu ug ain m tai en n t&

1. 2. IPO 3. Stru 4. Alg ctu De or re sk ithm Ch art Ch ec k

Modularization

Implementation

2. :Outline the solution (Structure Chart)

Larger problems require breaking the solution down into major tasks. If we take the next step from the IPO, we groups similar processing tasks into program modules and diagram it by using a structure chart.

Level 0

Example

Level 1 Task A

Task B

Task C

The main program is the driver program. It controls the program flow of the entire program. The main program asks a module to perform its task. When this occurs, control is temporarily given to that module. When the module finishes its task, control is given back to the main program.

Lynne Koenecke Illinois State University, ACS

33

Steeplechase

Run to Steeple

Jump Steeple

Jump Up

Jump Over

Jump Down

Run Steeple Race Run to Steeple Jump Steeple Pick Flower End Steeple Race

Run to Steeple and Jump Steeple will each have their own algorithms. The algorithms would be written based on their pre conditions, post conditions and the task they are asked to perform.

Lynne Koenecke Illinois State University, ACS

34

In tro d u c t i o n t o C P ro g r amm in g C is portable



portability is the ability to transfer a written program from one computer to another with few or no changes

•



C is fast and efficient



C is flexible high-level language, but allows manipulation of the inner workings of the computer

•

Ex am p l e C C o d e Line No. 1

/* Program to prompt for and print two numbers.*/

2

#include <stdio.h>

3

int num_1, num_2;

4

int main (void)

5

{

6

/*Input the first number*/

7

printf ("Enter a number between 1 and 100: ");

8

scanf ("%d", &num_1);

9

/*Input the second number*/

10

printf ("\nEnter another number between 1 and 100: ");

11

scanf ("%d", &num_2);

12

/*Print both numbers */

13

printf ("\n\nYou entered %d and %d.", num_1, num_2);

14

return(0);

15

}

(Line numbers are not entered in the C editor as part of the code. They are used here for reference only.)

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35

S am p le o u tp u t: Enter a number between 1 and 100: 25 Enter another number between 1 and 100: 50 You entered 25 and 50.

T h e P ro g r am C omp o n e n ts a n d D e f i n it i o n s main ( ) function - (lines 5 - 15) The main is the only component that is required in every C program. Usually program execution starts at the first statement in the main and ends at the last statement in the main. What is a function? A function is a section of code that is independent, performs a task, and has been given a name. When you reference a function's name, program control is sent to that function, the code is executed, and control returns to the calling function. Types of functions: • Library functions - part of the C compiler software package • User-defined functions - code written by the programmer Braces ({ }) (lines 5 and 15) Line 5 is an open brace and line 15 is a close brace. Every function must begin with an open brace and end with a closed brace. The group of statements between the braces is called a block. #include Directive -(line 2) instructs the C compiler to add the included file to your program during compilation. Also called header files. Header files define operations, symbols, values. Most C programs require the use of one or more include files. The sample program includes stdio.h, the header file which contains the standard input/output functions used in C.

Lynne Koenecke Illinois State University, ACS

36

Variable Definition (line 3) a variable is a name that is assigned to a storage location in memory. In C, you must define a variable before you can use it. The definition tells the compiler the name of the storage location and the type of data that will be stored there. You must follow specific C rules for naming variables. Comments - (lines 1, 6, 9, and 12) internal documentation of a program for the programmer (useful for the original programmer, but especially useful for the maintenance programmer months or years later). These statements are ignored by the compiler. In C the delimiters are the /* (to begin the comment) and */ (to end the comment) /* A single line comment */ int num_1, num_2; /* A partial line comment */ /* a multiple line comment */ Statements - (lines 7, 8, 10, 11, 13) instruction to the computer. Collectively, statements make up a program. Statements display information on the screen, accept input from the keyboard, perform logical and/or mathematical operations, read files, call functions, etc. printf() - library function that displays information on the screen. It can display a simple message or combine literal text with the contents of variables. scanf() - library function that reads data from the keyboard and assigns it to one or more program variables.

Lynne Koenecke Illinois State University, ACS

37

Va r i a b l e s A variable is a named storage location in the computer's random access memory (RAM).

Variables have a name, a type and a value.

Variable Names - you must follow the rules of C for naming variables. • The name can contain letters, digits, and underscores ( _ ). • The first character of a variable must be a letter. (the underscore is legal, but shouldn't be used as a first letter) • C is case sensitive (uppercase and lowercase letters are different to the C compiler) Num1 is not the same as num1. C looks at these two variable names as referring to two different storage locations. • C keywords cannot be used as variable names. • Variables can be 1 - 31 characters in length. Reserved words in C asm

auto

break

case

char

const

continue

default

do

double

else

enum

extern

float

for

goto

if

int

long

register

return

short

signed

sizeof

static

struct

switch

typedef

union

unsigned

void

volatile

while

Suggestions: •

Make variable names meaningful

•

Don't make them too long (leaves more room for typing errors)

•

Don't use single character variables except for counters

•

Use lowercase letters with underscores to separate words

Lynne Koenecke Illinois State University, ACS

38

Va r i a b l e D e c l a r a t i o n Before a variable can be used in C, it must be declared. Declaring a variable lets the compiler know that it needs to set aside a portion of main memory for use during the execution of your program. It tells the compiler the name that you are going to refer to the memory location as and the type of data that will be stored there. typename varname; int score_1; int count, number, start; /* declares three integer variables on one line */ float total_amount, percent; /*declares two float variables */

Variable Values - declaring a variable tells the compiler to set aside

memory space. The value in that space (the value of the variable you just named) is not defined. You only defined the name of the variable and the type of data to be stored. You must initialize the value to a known value by an assignment statement or initialize it at the declaration statement. If you do not initialize a variable by either of the above methods, you variable could contain "garbage". 1. Initializing numeric variables as you declare int count = 0; float percent = .05, taxrate = 37.2; 2. Initializing numeric variables with assignment statements percent = 12.3; amount = 43.25; number = 4; (Remember, these variables were declared before the assignment statements.)

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39

Numeric Variable Types - C has several different types of variables

for numeric data because different numeric values require different storage requirements in main memory. Using the correct data types ensures that your program runs as efficiently as possible. Integer variables • whole numbers (have no fractional parts) • -1, 0, 10, -12, 354 Floating-point variables • real numbers (have a fractional part) • -5.64, 0.564, 6.445, 7.2, -12.01 Within each of the two categories are more specific data types that deal with different memory requirements based on the size of the values. Variable Type

Keyword

Bytes Required

Range

character

char

1

-128 to 127

integer

int

2

-32768 to 32767

short integer

short

2

-32768 to 32767

long integer

long

4

-2,147,483,648 to 2,147,438,647

unsigned character

unsigned char

1

0 to 255

unsigned integer

unsigned int

2

0 to 65535

unsigned short integer

unsigned short

2

0 to 65535

unsigned long integer

unsigned long

4

0 to 4,294,967,295

single-precision floatingpoint

float

4

1.2E-38 to 3.4E38

double-precision floating point

double

8

2.2E-308 to 1.8E308

Table showing amount of bytes required to store different types of numeric variables on a 16-bit architecture PC.

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40

C o n st a n ts Another method of assignment is defining a constant value with the #define directive which is one of C's preprocessor directives. #define PI 3.14159 /* notice that there is no semi-colon */ The statement above defines PI as 3.14159 for the entire execution of the program. Anywhere in the program where PI is used, it is substituted for the value of 3.14159.

When using #define the name of the constant is written in all caps.

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41

Up p e rc a s e a n d L o w e rc a s e L e tte r s Great care must be taken when using case in letters. Num1, num1, and NUM1 are viewed as different identifiers by the C compiler.  All reserved words in C are lowercase.  #define preprocessor directives are all uppercase.

P ro g r am S ty l e Guidelines from improving readability of programs  Use meaningful variable names.  Use an underscore to separate words in a variable name lbls_per-sq_inch is much easier to read than lblspersqinch

Using white space in your programs What is white space? Why use it? Does the compiler care? • blank lines and spaces • use it to improve readability and appearance of your program • the compiler ignores it

Ex e c u t a b l e S t a tem e n ts Operations of a program are specified by executable statements that appear in the body of a program, following variable declarations. Each executable statement is translated by the C compiler into one or more machine language instructions that are copied to the object file and later executed.

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42

O r d e r o f C P ro g r am C omp o n e n ts /************************************************************* main comment block SEE the Comment Specifics in the back *

of your Lab Manual!!!!!

************************************************************/ Preprocessor Directives (#include, #define) Function Prototypes int main (void) { /* open brace which starts the function block*/ /*variable declarations*/ /*executable statements*/ return (0); }/*end of main program*/ /************************************************************ * user - defined function comment block ************************************************************/ function definition { /*variable declarations -if needed*/ /*executable statements*/ }

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43

D e ve l o p in g a C p ro g r am 1. Use an editor to type in and save your C source code. We will be using the editor in Turbo C++. The source code will be saved as filename.c. 2. Compile the program using a C compiler. If no errors occur then an object file is produced by the C compiler - filename.obj. If errors occur, they are displayed for you. Correct them, and try to compile again. 3. Link the program. If no errors are detected, then an executable file is created - filename.exe. 4. Execute the program. Here you should test to make sure that your program is free of logic errors and works exactly as how you intended it to. If there are errors, go back to step 1, revise the code and proceed through steps 2-4 again.

Source Code Editor

Preprocessed Source Code

Preprocessor

Object Code

Compiler

Executable Code Linker

External Items

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44

Ass i g nm en t St a t em en ts The = sign is used in C to place values into variables. The form is as follows: variable = constant;

or

variable = expression;

Ex: counter = 0; /* puts a value of 0 into the variable named counter */ Visually, in memory, the space allocated for counter now has a value of zero. counter 0 The value 0 is a constant. Expressions: When an expression is on the right side of the equal sign (=), the expression is first evaluated and then the value of that expression is assigned to the variable which is named on the left side of the equal sign (=). Ex: The variables number_1 and number_2 have been declared and assigned values of 5 and 6 respectively. number_1

number_2

5

6

sum

sum = number_1 + number_2; After the statement executes, the stored values are: number_1

number_2

sum

5

6

11

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45

S om e A r i thm et i c Op e r a t o r s Arithmetic Operator

Meaning

+

addition

-

subtraction or negation

*

multiplication

/

division

In p ut / Ou tp u t Op e r a t i o n s

C Input - scanf (); To get values into your program, the scanf function is used. The scanf function has two arguments. The first is the format control string and the second is the variable name preceded by an ampersand (&) which is the address of operator in C. Ex: scanf ("%d", &number_1); When this statement is executed, the cursor waits until the user enters a number and the enter key to proceed. After the enter key is pressed, the statement is completed. This example statement gets a decimal integer from the keyboard and assigns it to the address of number_1. scanf ("%d%f", &num_1, &average); /* accepts two integers separated by a space*/

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Prompting for scanf You should prompt the user to let them know what they are to enter before using the scanf function. printf ("Enter the first and second scores separated by a space: "); scanf ("%d%d", &score_1, &score_2);

C onv e r s i o n s Sp e c s f o r sc a n f ( ); The format strings should match the data type for scanf. Data type

scanf ( ) placeholder

char

%c

int

%d

float

%f

double

%lf

C Output: printf ( ); The printf function is used for C output to the screen. The following statement prints a line of text to the screen: printf ("This is my first C program."); The output is: This is my first C program.

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You can add a backslash (\), called an escape character, plus another character to indicate that printf should do something besides print the line of text. printf ("This is my first C program.\n"); printf ("A newline escape sequence was used."); The output is: This is my first C program. A newline escape sequence was used.

Common escape sequences Escape sequence

Description

\n

Newline. Positions the cursor at the beginning of the next line.

\t

Horizontal tab. Moves the cursor to the next tab stop.

\r

Carriage return. Positions the cursor to the beginning of the current line; does not advance to the next line.

\\

Backslash. Prints a backslash character in a printf statement.

\"

Double quote. Print a double quote character in a printf statement.

C on ve r s i o n s S p e c s f o r p r i n t f ( ); The format strings should match the data type for printf. Data type

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printf ( ) placeholder

char

%c

int

%d

float

%f

double

%lf

48

P r in t i n g Va r i a b l e s /* Addition program */ #include <stdio.h> int main(void) { int integer1, integer2, sum;

/* variable declarations */

printf ("Enter first integer\n");

/* prompts user */

scanf ("%d", &integer1);

/* reads an integer */

printf ("Enter second integer\n")

/* prompts user */

scanf ("%d", &integer2);

/* reads an integer */

sum = integer1 + integer2;

/* assignment of sum */

printf ("sum is %d\n", sum);

/* print sum */

return (0); /* indicate that program ended successfully */ } Program output

Enter first integer 45 Enter second integer 40 Sum is 117

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Algorithm: calculate_double get value to num_to_double double = num_to_double * 2 Print message with num_to_double and double End of calculate_double C Program: (Use the comments to be sure you include all necessary components.) /* include statement(s) */ #include <stdio.h> int main (void) { /* variable declarations */ int num_to_double; int double; /* executable statements - the translation of the algorithm */ clrscr(); printf (“Please enter a number to double “); scanf (“%d”, &num_to_double); double = num_to_double * 2; printf (“\n%d doubled is %d”, num_to_double, double); getch();

/* to hold the output on the screen */

return (0); } /* end of program */

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50

S im p le C o n t ro l S tr u c tu re s The if structure and if - else structure if (expression)

if (expression)

statement if true;

statement if true; else statement if false;

A compound statement or block in C must be surrounded with braces. if (expression)

if (expression)

{

{ statement;

statement;

.......

.......

statement;

statement;

}

} else { statement; ....... statement; }

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51

Nested If if (expression)

if (expression)

statement if true; else

statement; else if (expression)

if (expression) statement if true; else

statement; else statement;

statement if false;

R e p e t it i o n C o n t ro l St r u c tu re Counter-Controlled Loop - the for loop for (initial; condition; increment) statement; or for (initial; condition; increment) { statement; statement; ...... statement; } for (k=1; k<=10;k++) { .... }

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52

Graphics See the back of your ACS 168 lab manual for the graphics functions and explanations. Graphics have two modes: 1

Text •

2

must use #include

Graphics •

must use #include

Check your lab manual for code to include in every graphics program as well as how to change the Turbo C++ settings and change to the bgi directory.

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53

M a th in C C operation

Arithmetic

C expression

Operator

Algebraic expression

Addition

+

a+8

a+8

Subtraction

-

q-1

q-1

Multiplication

*

kr

k*r

Division

/

x/y or x/y or x÷y

x/y

Modulus

%

r mod y

r%y

Integer Division C evaluates the expression 8 / 3 to have the value of 2. Both 8 and 3 are integers and the result will also be an integer. C divides and drops the fractional part of the answer. 9/7 = 1

10/3 =

12/5 =

61/2 =

Modulus Gives the remainder after integer division. 5%2=1 How did we get that answer? 12 % 2 =

14 % 2 =

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5/2 = 2 R 1 16 % 3

1 is the modulus 25 % 6 =

54

O r d e r o f Op e r a t i o n s When C evaluates expressions, it follows rules of operator precedence. Operator(s) Operation(s)

Order of evaluation (precedence)

( )

Parentheses

1st to be evaluated. If there are parentheses inside parentheses (nested parentheses), the inner most parentheses are evaluated first, then continue out to the outermost parentheses.

+, -, ! (not)

unary

2nd to be evaluated.

*, /, or %

Multiplication

3rd to be evaluated. If there is more than one of these operators, C evaluates from left to right.

Division Modulus + or -

Addition

Last. If there is more than one of these operators, C evaluates from left to right.

Subtraction

x = q - 8 * y / 4 + 16 Order of operation

3

1

2

4

x = 4 - 8 * 2 / 4 + 16 4 4

16

-

/ 4 4

0

+ 16 + 16 + 16

16

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55

Ty p e C o n v e r s i o n s All of C's data objects have a specific type. The logic of programs sometimes requires that different types be combined in expressions and statements. Sometimes C automatically handles these different types. At other times, the conversion must be made by the programmer.

Automatic type conversions - performed automatically by the C compiler.

• When a C expression is evaluated, the resulting value has a particular data type. sum = integer_1 + integer_2; *if integer_1 and integer_2 are typed int, then sum will be int result = number + average; *if number is an integer and average is a float, then the result is a float because of the following: When the above is evaluated the result has the same type as its most comprehensive component. char

int

Least comprehensive

long

float

double

Most comprehensive

int = int + int; float = float + float; float = int + float; example: x/y if x is an int and y is a float, evaluating the expression causes a copy of x to be promoted to float before it is evaluted

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56

Explicit type conversions - occurs when the programmer instructs the computer to convert a value from one type to another. Using typecasts A typecast uses the cast operator explicitly to control type conversions in a program. A typecast consists of a type name, in parentheses, placed before an expression. Example: int integer;/*integer is declared*/ (float) integer; /*typecasts integer to float*/

Variable

Data Type

Value

test1

int

90

test2

int

75

total

int

4

a

int

3

b

int

5

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Problems- evaluate as the C compiler would. 1.

What is the product of 5 and 7 divided by 2?

Answer

2.

Data type

total = a2 + b2

Answer

Data type of total

3. average = (test1 + test2)/2 Answer

4.

Data type of average

percentage_of_difference = (test1 - average) / average * 100

Answer

Data type of percentage of difference

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58

S w i t c h (M u lt ip l e -S e l e c t i o n S tr u c tu re ) switch (controlling expression) { case c1: any number of statements; break; case c2: any number of statements; break; default: any number of statements; }

• Use when the selection is based on a single variable or simple expression (controlling expression). • The value of the controlling expression should evaluate to int or char, not double. • Maximum of 10 cases • The controlling expression is evaluated, then the list of case labels is searched until one label that matches the value of the controlling expression is found. • Statements the follow the matching case label are executed until a break statement is encountered. The break causes an exit from the switch statement. • If no match is found, execution is transferred to the statement following the optional default label. • If no match is found and there is no default label, execution passes to the first statement following the switch statement's closing brace.

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/* Demonstrates the switch statement */ #include <stdio.h> void main () { int reply; printf ("Enter a number between 1 and 5: "); scanf ("%d", &reply); switch (reply) { case 1: printf ("You entered 1."); break; case 2: printf ("You entered 2."); break; case 3: printf ("You entered 3."); break; case 4: printf ("You entered 4."); break; case 5: printf ("You entered 5."); break; default: printf ("Out of range, try again."); } }

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60

Switch is used quite often to process menu choices that a user makes. gotoxy (____ , ____) is used to position text on the screen The screen measures as follows in text mode: 80 columns (x value)

24 rows (y value)

/************************************************** * Function to print a menu using gotoxy **************************************************/ void print_menu (void) { gotoxy (38,7); printf ("Menu Choices"); gotoxy (32,9); printf ("1. Enter Data"); gotoxy (32,10); printf ("2. Process Information"); gotoxy (32,11); printf ("3. Exit"); gotoxy (32, 15); printf ("Enter your choice: ");

}

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61

Ch a r a c t e r D a t a Another standard data type in C is type char. Variables of type Char can be used to store any single character value. Variable declaration char letter_1, letter_2, letter_3; scanf (“%c%c%c”, &letter_1, &letter_2, &letter_3); /* User enters Bob and presses return*/ letter_1

letter_2

letter_3

B

o

b

Character data is frequently used to get a user choice in from a menu. char choice; choice = getch(); We have previously used getch() to hold the screen for viewing output . If you assign getch(); to a character variable, the key that was hit by the user is stored. The enter key is stored as ‘/n’ getche(); /* The e echoes (repeats) the user’s choice to the screen.

Screen Design Be sure to read the guidelines for screen design for Lab 10. Materials are on reserve in the Library under your instructor’s name.

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62

Functions Programmer-defined functions are blocks of code that perform a specific task and may return values to the calling program. In C, functions are the same as modules. Functions allow the programmer to modularize the program.

Why use functions? • Software reusability - the same code can be utilized more than once in a program. • Makes programs more manageable, easier to understand, debug, and test.

Parts of a function: • Function prototype • Function call • Function definition All functions must have all three parts.

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63

Function prototype tells the compiler: • type of data returned by the function • number of arguments the function expects to receive • data types of the arguments • order in which the arguments are expected placed before the main function as follows: return-value-type function_name (argument list, . . .); argument list consists of data types in order, variable names are optional Default return-type is int, if nothing is to be returned, void is used.

Function call invokes the function: printf ("Half of %d is %d.", x, half_of(x)); /*function call with argument of x, nothing is returned*/ y=half_of(x); /*function call with argument of x, 1 value is returned and placed in y*/

print_half (y); /*function call with argument of y, nothing is returned*/ print_header ( ); /*function call with no argument(s), nothing is returned*/

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64

Function definition tells the compiler: • type of data to be received by the function • number of parameters the function expects to receive • name of parameter(s) the function receives • data types of the parameters • order in which the parameters are expected placed as a header before the function's lines of code as follows: return-value-type function_name (parameter list, . . .) parameter list consists of data types in order, and variable names Default return-type is int, if nothing is to be returned, void is used. Also, notice that there is no semi-colon at the end of the line just as in the main.

The format of a function is: return-value-type function_name (parameter list, . . .) { declarations statements }

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65

/* A programmer-defined square function */ #include <stdio.h> int square (int);

/*function prototype*/

int main (void) { int x; for (x = 1; x <=10; x++); printf ("%d ", square (x)); /*calls the function*/ return (0); } /* Function definition */ int square (int y) { return y * y; }

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66

P a ss i n g A r gum en ts You can pass arguments two ways. 1. By Value or

2. By Address

Passing by Value • The value of the variable is passed through the argument list to the receiving function. • Passing a variable by value protects it's content. /*passing a variable by value */ #include <stdio.h>

Program output: Please enter a number: 24

void half (int);

Your value halved is 12. In main ( ), j is still 24.

int main (void) { int j; printf ("Please enter a number: "); scanf ("%d", &j); half (j); /*function call passes a copy of the contents of j to half */ printf ("In main ( ), j is still %d.\n", j); return (0); } /*end main */ void half (int j) { j = j/2; printf ("Your value halved is %d.\n", j); } /*end half*/

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67

Passing by Address • The memory address of the variable is passed to the receiving function from the calling function. • If the value of the variable is changed in the receiving function, it is also changed in the calling function. To pass a variable by address, you must: • put an & operator in from of the variable name in the argument list of the calling function • put an * (dereferencing) operator in front of the variable everywhere it is referenced in the receiving function /*passing a variable by address */ #include <stdio.h>

Program output: Please enter a number: 24

void half (int *);

Your value halved is 12. In main ( ), j is now 12.

int main (void) { int j; printf ("Please enter a number: "); scanf ("%d", &j); half (&j); /*function call passes the address j to half */ printf ("In main ( ), j is still %d.\n", j); return (0); } /*end main */ void half (int *j) { *j = *j/2; printf ("Your value halved is %d.\n", *j);

} /*end half*/

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68

E x amp l e s o f P os s ib l e F o rm s F u n c ti o n s C a n Take Returns No Result void print_header (); /* function prototype */ print_header(); /*function call*/ /****************************** *This function displays a header ******************************/ void print_header(void)

print_header

{ printf ("Report title"); }

With Arguments void print_summary (int, int); /* function prototype */ print_summary(count, total); /*function call*/ /******************************

count

*This function displays a summary

total

******************************/ void print_summary (int count, int total) { double average;

print_summary

average = (float) count/total; printf ("The count is: %d\n", count); printf ("The total is: %d\n", total); printf ("The average is: %d\n, average);

}

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69

Returns a Single Result int sum (int, int); /* function prototype */ answer = sum(number1, number2); /*function call*/ /******************************

number1

*This function adds 2 numbers

number2

answer

******************************/ int sum (int num1, int num2) {

sum

int total; total = num1 + num2; return (total); }

Returns Multiple Results void calculate_total (double, double, double*, double*, double* ); /* function prototype */ calculate_total (item1, item2, &subtotal, &tax, &total); /*function call*/ /*************************************** *This function calculates subtotal, tax, and total ***************************************/ void calculate_total (double item1, double item2, double *subtotal, double *tax, double *total )

subtotal item1

tax

item2

total

{ *subtotal = item1 + item2;

calculate_total

*tax = *subtotal * .07 *total = *subtotal + *tax;

}

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70

C omp ou n d Ex p re ss i o n s & N e ste d I f s Logical Operators Sometimes, you must ask more than one question to evaluate an expression. For example, "If it is 7:00 a.m. and a weekday and not a vacation day, ring the alarm." In C, you must use a combination of logical operators to ask multiple questions. Operator

Symbol

AND

&&

Example expression1 && expression2

OR

||

expression1 | | expression2

NOT

!

!expression1

Expression

Evaluates As

(exp1 && exp2)

True (1) only if both exp1 and exp2 are true; false (0) otherwise.

(exp1 | | exp2)

True (1) if either exp1 or exp2 is true; false (0) only if both are false.

(!expr1)

False (0) if exp1 is true; true (1) if exp1 is false

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71

Expression

Evaluates As

(5 = = 5 ) && (6 != 2)

True (1) because both operands are true

(5 > 1) | | (6 < 1)

True (1) because one operand is true

(2 = = 1) && ( 5 = = 5)

False (0) because one operand is false

!(5 = = 4)

True (1) because the operand is false

Precedence of Logical Operators ()

highest

! - (unary) * / % + - (binary) < <= > >= = = != && || =

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lowest

72

Truth Tables (T = true, F = false) x

y

x && y

F

F

F

F

T

F

T

F

F

T

T

T

x

y

x||y

F

F

F

F

T

T

T

F

T

T

T

T

x

!x

F

T

T

F

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73

F o rm a tti n g Num e r i c a l Ou tp u t int • %d prints the value exactly as it is • the field width, placed between the % and the d indicates the number of columns to be displayed. • default is right justified • use a - to left justify • a negative sign is counted in the field width • the field expands as needed Examples: printf("%d%d\n",254,842); printf("%1d%2d\n",254,842); printf("%3d%4d\n",254,842); printf("%4d%5d\n",254,842); printf("%-4d%-5d\n",254,842); printf("%-6d%-7d%d\n",254,842, 324); Output (b = blank space) 254842 254842 254b842 b254bb842 254b842bb 254bbb842bbbb324

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74

float, double •

%f always prints with 6 decimal place

•

format: %n.mf •

n is the total field width

•

m is the number of decimal places

n=6 •

the decimal point and negative sign are counted in the total width

•

if there is no whole number, a 0 always prints

• fractional parts are rounded if the field is smaller than the assigned number •

if the format %.mf is used, it will print with no leading blanks

•

a number is right-justified unless a minus sign is placed immediately after the %

Examples: printf("%f%f\n",254.0,842.0); printf("%6.4f%8.4f\n",254.0,842.0); printf("%.2f%.4f\n",254.0,842.0); printf("%3.2f%6.2f\n",254.0,842.0); printf("%-15.4f%-9.4f\n",254.0,842.0); printf("%-8.0f%-9.0f\n",254.0,842.0); Output (b = blank space) 254.000000842.000000 254.0000842.0000 254.00842.0000 254.00842.00 254.0000bbbbbbb842.0000 254bbbbb842bbbbbb Lynne Koenecke Illinois State University, ACS

75

Arrays Data Structure - grouping of related data items in memory. Using a data structure, you can process data individually or as a whole. Array - data structure used for storage of a group of related items that are of the same data type.

Declaring Array structures in C ❏ Assign one name to a group of items. These items will be stored in adjacent memory locations. ❏ Declare the data type, name and number of memory locations to be used float score [5]; *Many times a #define is used to assign the size of an array making modifications much easier if the array size changes. #define SIZE 5 float score [SIZE]; Referencing Arrays: subscripts or indexes are used to reference individual items of an array called elements. C starts referencing arrays with 0. score [0] score [1] score [2] score [3] score [4]

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76

Getting Values into Array Elements There are 3 ways to assign values to the elements of an array 1. Initializing arrays in the variable declaration statement. 2. Reading input values into the array from the keyboard or file. 3. Assignment statements. Initialization float score [SIZE] = {90, 84, 76, 100, 64}; score [0]

90

score [1]

84

score [2]

76

score [3]

100

score [4]

64

Reading input values in via keyboard for (j = 0; j<5;j++) { printf ("Please enter a score "); scanf ("%f", &score[j]); } Assignment Statements difference [1] = score [1] - average; /*The average has been found by adding up all of the array elements and dividing by the number of elements.*/

Lynne Koenecke Illinois State University, ACS

77

Advantages of Using Arrays ❏ You can reference many items by one name. This reduces the number of different variable names that you need for your program. ❏ You can use the same code to reference different memory locations by changing the array subscript by using a variable name for the subscript. ❏ You can store multiple data items for use later in the program. #define SIZE 25; int main ( ); {

score [0]

90

int j;

score [1]

84

sum = 0;

score [2]

76

float average;

score [3]

100

float score [SIZE] = {90, 84, 76, 100, 64};

score [4]

64

sum

90

float difference [SIZE]; for (j = 0; j<5; j++)

174

{

250

sum = sum + score [j];

350

}

414

average = sum / 5;

average

82.8

for (j = 0; j<5; j++)

difference [0]

7.2

{

difference [1]

1.6

difference [2]

-6.8

difference [3]

17.2

difference [4]

18.8

difference [j] = score [j] - average; } }/*end main*/

Lynne Koenecke Illinois State University, ACS

78

Passing Arrays ❏ Arrays cannot be used in the return of the function. ❏ Arrays are passed by address by default. ❏ To override this, use the word const in front of the declaration in the parameter list. Function prototype void function_a (int [ ]); Function call fuction_a (score); Function definition void function_a (int score [ ]) { . . }

Lynne Koenecke Illinois State University, ACS

79

S o r t i n g A r r a y E l em en ts There are times when the elements of an array need to be sorted. Numbers or names may need to be put in ascending or descending order so that they can be searched or printed in order. There are several sorting methods. We will discuss the bubble sort and selection sort.

Bubble Sort 1. Decide if the array should be sorted in ascending or descending order. 2. Compare adjacent elements in an array and exchange the values when they are out of order. 3. One complete time through all array elements is referred to as a pass through the array. At the end of the first pass, the largest value is in the last element of the array (if you are sorting in ascending order). 4. The maximum number of passes through an array to sort the elements is the number of elements minus 1. The minimum number of passes is 1.

Selection Sort 1. Find the smallest element in the array. Exchange that element with the one in the first position (this is for ascending order). 2. Starting from the second element, find the smallest element in the array and exchange that element with the element in the second position. Continue until the array is sorted.

Lynne Koenecke Illinois State University, ACS

80

Bubble Sort Example Original unsorted array score: score [0]

80

score [1]

70

score [2]

50

score [3]

90

score [4]

60

Before pass

Swapping During Pass

score [0]

80

80

score [1]

70

70

80

score [2]

50

Swap

50

80

score [3]

90

Swap

90

score [4]

60

No Swap

After pass score [0]

70

score [1]

50

score [2]

80

90

score [3]

60

60

score [4]

90

score [0]

50

score [1]

70

score [2]

60

Swap score [0]

70

70

score [1]

50

50

70

score [2]

80

Swap

80

80

score [3]

60

No Swap

60

80

score [3]

80

score [4]

90

Swap

90

score [4]

90

score [0]

50

score [1]

60

score [2]

70

No Swap score [0]

50

50

score [1]

70

70

70

score [2]

60

No Swap

60

70

score [3]

80

Swap

80

80

score [3]

80

score [4]

90

No Swap

90

score [4]

90

No Swap

Lynne Koenecke Illinois State University, ACS

81

Selection Sort Before pass

Swapping During Pass

After pass

score [0]

80

Smallest = 50 (element 2)

score [0]

50

score [1]

70

Exchange with the first element

score [1]

70

score [2]

50

score [2]

80

score [3]

90

score [3]

90

score [4]

60

score [4]

60

score [0]

50

score [0]

50

score [1]

70

score [1]

60

score [2]

80

Smallest of elements 1 - 4 = 60

score [2]

80

score [3]

90

Exchange with the second element

score [3]

90

score [4]

60

score [4]

70

score [0]

50

done

score [0]

50

score [1]

60

done

score [1]

60

score [2]

80

Smallest of elements 2 - 4 = 70

score [2]

70

score [3]

90

Exchange with the third element

score [3]

90

score [4]

70

score [4]

80

score [0]

50

done

score [0]

50

score [1]

60

done

score [1]

60

score [2]

70

done

score [2]

70

score [3]

90

Smallest of elements 3 - 4 = 80

score [3]

80

score [4]

80

Exchange with the fourth element

score [4]

90

done

S e a rc h in g a n A r r a y Linear Search (Sequential Search) Searching the array item by item, quitting when the target item is found Algorithm target not found start with initial array element while (target is not found and there are more elements) if (current element matches target) set flag to indicate target found else advance to the next element if target found return target index as the result else return -1 as the search result (target not found)

/*************************************************************** *Search for the target item of an array *Returns the index of the target or not_found *Pre-conditions: target and first n elements are devined & n>0 * array is the array, target is the value to search for, n = num_elements ***************************************************************/ int search (const int array [ ], int target, int n) { int k; int found = 0; /* flag to indicate whether the target has been found */ int where;

/*index where target found or not found*/

/*compare each element to the target */ k = 0; while (!found && k < n) /* loop stops at either the last element or on a value that matches target*/ { if (array [k] = = target) found = 1; /* if the target has been found, the flag is set to found or 1*/ else ++k; } /*returns index of element that matched target or not found */ if (found) /*remember true = 1 */ where = k; /* k is the index number where the loop stopped */ else where = 0; return (where); }

Binary Search Searching a sorted array. Takes the array, divides it in half, searches the appropriate half and "throws away" the other half. The half kept is then split and the procedure is repeated until the target item is found.

Algorithm bottom = subscript of the initial array element

array[ ] element 0

5

1

8

2

12

3

20

4

32

5

35

6

36

found = true

7

40

record position

8

60

9

65

10

68

11

70

12

75

top = subscript of the last array element found = false while (target not found) calculate middle position if (the element at middle is the target then)

else if (element at middle > target) top = middle - 1 else bottom = middle + 1

Looking for 36

int binary_search (int array [ ], int size, int item) { int middle, where, botom, top, found; bottom = 0; top = size; found = 0; while (!fount && bottom <= top) { middle = (bottom + top)/2; if (array [middle] = = item) { found = 1; where = middle; } else if (array[middle]>item) top = middle - 1; else bottom = middle + 1; } if (found) return (where); else return (-1); /*indicates unsuccessful*. }

Ch a r a c t e r v s. S tr i n g s char •

variable that stores a single character of information

•

placed between two apostrophes 'c' or 'C' or 'm' or 'M', etc.

•

use %c for printf or scanf

•

getchar - reads a character from keyboard

•

putchar - displays a character to the screen

Buffers •

buffers stores characters in s special location in main memory to be sent to secondary storage or they can be brought in from secondary storage

•

there is a stdin buffer and a stdout buffer

•

when the buffer fills, the computer flushes to a peripheral device

•

you can force the buffer to flush by fflush (include conio.h) fflush(stdin); flushes the stdin buffer

/*code with no flush*/ #include <stdio.h> void main() { char a_character; clrscr(); printf ("Enter a character: "); a_character = getchar(); printf ("\nThe character you just entered is: %c\n",a_character); printf ("Enter another character: "); a_character = getchar(); printf ("\nThe character you just entered is: %c\n",a_character); getch(); return 0; }

/*code that flushes stdin*/ #include <stdio.h> #include void main() { char a_character; clrscr(); printf ("Enter a character: "); a_character = getchar(); printf ("\nThe character you just entered is: %c\n",a_character); fflush(stdin); printf ("Enter another character: "); a_character = getchar(); printf ("\nThe character you just entered is: %c\n",a_character); getch(); return 0; } This code flushes the input buffer and allows you to grab the next character.

C d e f in e d c h a r a c t e r f u n c t i o n s (uses #include ) Function

returns TRUE if argument is:

tolower

returns the lowercase letter of its character argument

toupper

returns the uppercase letter of its character argument

isalnum

letter or digit

isalpha

letter

iscntrl

control character

isdigit

digit

isgraph

printable character, but not white space

islower

lowercase letter

isprint

printable character, including blank

ispunct

printable character other than letter, digit, or white space

isspace

space, newline, tab, form feed, carr

isupper

uppercase letter

strings • series of characters dealt with as a single unit • can include letters, digits, and +, -, *, /, $, and other special characters • enclosed in double quotes • treated as an array of characters (char) is the ASCII value 0 (null or '\0') follows the last meaningful character The end of all strings are marked with null zero '\0' by C You must account for this in your delcaration.

'x' - takes one byte of memory

x

"x" - takes two bytes of memoryx\0 char month[10]; If the month "September" were stored in memory and the address of month it would look like the following [0]

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

S

e

p

t

e

m

b

e

r

\0

*Remember amount of storage required is the number of non-null characters + 1

There are only 3 ways to assign string values: 1. Initialization 2. One character at a time. 3. Using C's strcpy ( ) function

(use #include <string.h>

1. Initialization char month[10] = "January";

month = "January"; /* This is illegal */ The only time an = sign can be used is in initialization.

2. One character at a time #include <stdio.h> void main() { char mystring[20]; clrscr(); mystring[0] = 'H'; mystring[1] = 'e'; mystring[2] = 'l'; mystring[3] = 'l'; mystring[4] = 'o'; mystring[5] = '\0'; printf ("%s",mystring); printf ("\n"); printf ("%c",mystring[5]); getch( ); } Output Hello   (represents where the cursor is after the code is executed)

3. C's strcpy( ) function - must use #include <string.h> strcpy (month, "April");

A r r a y s o f S tr in g s If you want to store several strings under the same name, you must use an array of strings. The are declared as follows: char

months [12][10];

data_type

array_name [#elements][max_string_length + 1];

[0] [0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

Memory would look like this after the values have been assigned. [0]

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[0]

J

a

n

u

a

r

y

\0

[1]

F

e

b

r

u

a

r

y

\0

[2]

M

a

r

c

h

\0

[3]

A

p

r

I

l

\0

[4]

M

a

y

\0

[5]

J

u

n

e

\0

[6]

J

u

l

y

\0

[7]

A

u

g

u

s

t

\0

[8]

S

e

p

t

e

m

b

e

r

[9]

O

c

t

o

b

e

r

\0

[10]

N

o

v

e

m

b

e

r

\0

[11]

D

e

c

e

m

b

e

r

\0

[9]

\0

I/O of strings Function Call

Write to

Add '\n' ?

Error Return

printf ("%s", string);

stdout

no

negative

puts (str);

stdout

yes

EOF

fprintf (outfile_ptr, "%s", string);

output file

no

negative

fputs (str, outfile_ptr);

output file

no

EOF

#include <stdio.h> void main() { clrscr(); printf (" s %s\n","123456789"); printf ("15s%15s\n","123456789"); printf ("20s%20s\n","123456789");

Output s 123456789

printf ("-12s %12s\n","123456789");

15s

getch();

-12s 123456789

}

20s

#include <stdio.h> void main() { /*Demostrates that the control string is just a string*/ char format [] = "%s\n"; char message [] = "hello"; clrscr(); printf (format, message); getch(); } Output hello

123456789 123456789



F i l e s in C Files defined C performs input and output by streams. The standard input and output are the keyboard and monitor respectively. Disk file streams work basically the same way.

Text Files • A text (stream) file is a collection of characters stored under the same name in secondary memory (i.e. on a disk). • Each line has 0-255 characters. • The line is ended by a special character called an end of line character or '\n'. A line is not a string because it is not terminated with '\0'. • The CR-LF is translated into \n as it is being read from a file in a C program. • The \n is translated into CR-LF as it is being written to a file in a C program. • Data is sent one character at a time.

Record or Binary Files • Data is written and read unchanged. • Null and EOL characters have no special significance. • Used for high data volume. • Blocks of data are transferred by each I/O operation.

Indexed Files • Allow for fast access to any record on a file. • Each record is indexed and you don't have to go through all records to access the record you are looking for.

File Names You must name files when dealing with disk files. The DOS naming convention must be used in Turbo C++. You will be working with files on your floppy disk. Files should be named a:\filename.txt. (The file name must be 8 characters or less and the extension must be 1 to 3 characters.)

possible file names

a:payroll.dat a:words.rpt a:report.rpt a:timecard.in

Declaring Files Before a file can be used for input or output, you must declare a file pointer variable and give it a value. The stidio library function fopen prepares the file for input or output before permitting access. A file pointer's data type is FILE *. A declaration statement for a file to be used in C would look like one of the following: FILE * infile_ptr; FILE * in_ptr; FILE * out_ptr; FILE * fp;

Opening a File stream The file must be opened before a program can read from it or write to it. The declarations above only declare space in memory. No value has been assigned. The library function fopen() points to the file pointer and checks to see if the filename is valid. fopen requires 2 arguments. Both arguments are strings and can be displayed in the function as literals or variables. fp = fopen (filename, mode);/* both filename and mode have been declared and have values*/ infile_ptr = fopen ("a:students.txt","r"); out_ptr = fopen ("a:payroll.dat","w");

Errors There are several possibilities for file error. A few of those are: • The program is trying to write to a write-protected disk. • The program is trying to read a file that is not on the disk. • The pathname is incorrect. If a file does not successfully open the value assigned is NULL. Code should always be written after an fopen to verify that the file was opened correctly. if (infile_ptr == NULL) { printf("students.txt does not exist.\n"); exit (1); /* terminates the program*/ } The statements can be combined in one if statement: if ((in_ptr= fopen ("clients.txt", "r")) = = NULL)

printf("File could not be opened.\n"); else ......

Modes

Values of Mode Mode

Meaning

r

Open the file for reading only. If the file doesn't exist, fopen() returns NULL.

w

Open the file for writing. If a file of the specified name does not exist, it is created. If the file already exists, existing data will be erased.

a

Open the file for appending. If a file of the specified name doesn't exist, it is created. If the file already exists, new data is appended (added) to the end of the file.

r+

Open the file for reading and writing. If a file of the specified name does not exist, it is created. If the file already exists, new data is added at the beginning of the file, overwriting existing data.

w+

Open the file for reading and writing. If a file of the specified name does not exist, it is created. If the file already exists, it is overwritten.

a+

Open the file for reading and appending. If a file of the specified name does not exist, it is created. If the file already exists, new data is appended to the end of the file.

wb

Open a binary file for writing.

rb

Open a binary file for reading.

Closing a File The function fclose() is used to close a file when the program no longer needs the use of the file. fclose (infile_ptr); fclose (out_ptr); The file argument must be an opent file.

File I/O Text Files

Read

Stop reading with

Error return

Function Call

Read from

Skip White Space before?

scanf ("%s", string);

stdin

yes

word

white space

EOF

gets (string);

stdin

no

line

'\n' (discard)

NULL

fscanf (infile_ptr, "%s", string);

input file

yes

word

white space

EOF

fgets (str, n, infile_ptr);

input file

no

line

'\n' (keep), EOF, or n-1 characters

NULL

Function Call

Write to

Adds ‘\n’?

Error return

printf (“%s”, string);

stdout

no

negative

puts (string);

stdout

yes

EOF

fprintf (outfile_fp, “%s”, string);

output file

no

negative

fputs (string, outfile_fp);

output file

no

EOF

fprintf - functions similar to printf. Output goes to a file, rather than the monitor fprintf (outfile_ptr, "Price = %.2f, tax = $%.2f\n", price, price * TAX_RATE);

fputs - writes data to a file fputs (string, outfile_ptr); fscanf - functions similar to scanf. Takes input from a specified file. fscanf (infile_ptr, "%f", &price);

fgets - functions similar to gets. Output goes to a file, rather than the monitor. fgets (str, 20, infile_fp); /* fgets puts characters in the array str until it encounters and EOR or ‘\n’ or after reading 19 characters */

feof - file end of file detects the end of a file. If there is more data in the file a value of zero (false) is returned. if (feof (infile_ptr)) . . /* the body of the if statement executes if there is data in the file*/ -evaluates to true or false

File I/O Binary Files fwrite - writes information to a file in binary fwrite (&EmployeeRec, sizeof (employee_t),1, employ_ptr); parameters are:

1. starting address of area in memory that contains the data 2. number of bytes in an item, such as the number of bytes in a structure, to be written 3. number of data, such as the number of records 4. the file pointer

fread - used to read a record or an array of records all a once fwrite (&EmployeeRec, sizeof (employee_t),1, employ_ptr); parameters are:

1. starting address of area in memory to receive data 2. number of bytes in an item, such as the number of bytes in a structure, to be read 3. number of data, such as the number of records to be read 4. the file pointer

feof - file end of file detects the end of a file. If there is more data in the file a value of zero (false) is returned. if (feof (infile_ptr)) . . /* the body of the if statement executes if there is data in the file*/ -evaluates to true or false

Recursion A function that calls itself is said to be recursive. The ability to invoke itself enables a recursive function to be repeated with different parameter values. You can use recursion as an alternative to iteration (looping). The recursive algorithms that we write will generally consist of an if statement with the following form: if this is a simple case solve it else redefine the problem using recursion

Recursive factorial Funcion /* *

Compute n! using a recursive definition

*

Pre:

n>=0

*/ int factorial (int n) { int ans; if (n == 0) ans = 1; else ans = n * factorial (n-1); return (ans); }

Trace of:

fact = factorial (3);

fact = factorial (3);

n is 3 ans is 3 * factorial (2) return (ans)

n is 2 ans is 2 * factorial (1) return (ans)

n is 1 ans is 1 * factorial (0) return (ans)

n is 0 ans is 1 return (ans)

Iterative factorial Function /* *

Compute n! using an iteration

*

Pre:

n>=0

*/ int factorial (int n) { int i, product = 1; /* Compute the product n x (n-1) x (n-2) x. . x 2 x 1 */

for (i=n; i>1; i=i-1) { product = product * i; } /*Return function result */ return (product); }