Unit 7 C Intro

C Programming Introduction ME 325 Spring, 2007

C Compiler • Below is a link for a free C/C++ compiler • http://www.bloodshed.net/dev/devcpp. html

Overview • History and Philosophy of C • Program Development Cycle • Compiler • First program • printf

History • The initial development of C occurred at AT&T Bell Labs between 1969 and 1973; It was named "C" because many of its features were derived from an earlier language called "B" . • By 1973, the C language had become powerful enough that most of the Unix kernel, originally written in PDP-11 assembly language, was rewritten in C. • In 1978, Dennis Ritchie and Brian Kernighan published the first edition of The C Programming Language. The version of C that it describes is commonly referred to as "K&R C". • The second edition of the book covers the later ANSI C standard. – K&R introduced several language features:

• struct data types. long int data type, unsigned int data type, The =operator was changed to -=

• During the late 1970s, C began to replace BASIC as the leading microcomputer programming language. During the 1980s, it was adopted for use with the IBM PC

Philosophy • C is a minimalistic programming language. • Does not require extensive run-time support. • Encourage machine-independent programming, and portably • Provide low-level access to memory. As a result, C code is suitable for many systems-programming applications that had traditionally been implemented in assembly language. The language has become available on a very wide range of platforms, from embedded microcontrollers to supercomputers.

Characteristics • Small size • Extensive use of function calls • Loose typing • Structured language • Low level (BitWise) programming readily available • Pointer implementation - extensive use of pointers for memory, array, structures and functions. • Small set (around 30) of reserved keywords

Program Development Cycle Program Performing a Task • Determine Output • Identify Input • Determine process necessary to turn given Input into desired Output

Pseudocode • Pseudocode is a compact and informal high-level description of a computer programming algorithm that uses the structural conventions of programming languages, but omits detailed subroutines, variable declarations or language-specific syntax. • Example if Credit Card Valid Process valid credit card routine else Process invalid credit card routine

end if

Flowchart • A flow chart is a schematic representation of an algorithm or a process. • Symbols

– Start and end symbols, represented as ovals or rounded rectangles – Arrows, showing what's called "flow of control" in computer science. – Processing steps, represented as rectangles. Examples: "Add 1 to X"; "replace identified part"; "save changes" or similar. – Input/Output, represented as a parallelogram. Examples: Get X from the user; display X. – Conditional (or decision), represented as a diamond (rhombus). These typically contain a Yes/No question or True/False test. This symbol is unique in that it has two arrows coming out of it. – A Data File represented by a cylinder

Program Development Cycle Write Pseudocode Program Source Code Compile/ Link

Executable

Test

Document

Libraries

C Compile Model • C is compiled language. This means that once you write your C program, you must run it through a C compiler to turn your program into an executable that the computer can run (execute). • The C program is the human-readable form, while the executable that comes out of the compiler is the machine-readable

The C Compilation Model The Preprocessor • The Preprocessor accepts source code as input and is responsible for

– removing comments – interpreting special preprocessor directives denoted by #. • #include -- includes contents of a named file. Files usually called header files. e.g • #define -- defines a symbolic name or constant. Macro substitution. • #define MAX_ARRAY_SIZE 100

Compiler • The C compiler translates source to assembly code. The source code is received from the preprocessor. Assembler • The assembler creates object code. (.OBJ on MSDOS) to indicate object code files. Link Editor • If a source file references library functions or functions defined in other source files the link editor combines these functions (with main()) to create an executable file.

Hello World, a Program is born #include <stdio.h> int main() { printf(“Hello World\n"); return 0; }

Hello World, Explanation • #include <stdio.h>, this line includes the "standard I/O library" into your program. The standard I/O library lets you read input from the keyboard (called "standard in"), write output to the screen (called "standard out"), process text files stored on the disk, and so on. C has a large number of standard libraries like stdio, including string, time and math libraries. A library is simply a package of code that someone else has written to make your life easier. • The line int main() declares the main function. Every C program must have a function named main somewhere in the code. At run time, program execution starts at the first line of the main function. • In C, the { and } symbols mark the beginning and end of a block of code. In this case, the block of code making up the main function contains two lines. • The printf statement in C allows you to send output to standard out (the screen). The portion in quotes is called the format string and describes how the data is to be formatted when printed. The format string can contain string literals such as “Hello World" symbols for carriage returns (\n), and operators as placeholders for variables.

printf ( const char * format, ... ); • Output formatted string to the standard output (stdout). • The string constant format provides a description of the output, with placeholders marked by "%" escape characters “\”, to specify both the relative location and the type of output that the function should produce.

%[flags][width][.precision][leng th]specifier Specifier

Output

Example

c

Character

A

d or i

Signed decimal integer

392

e or E

Scientific notation using e/E character

3.92e+2

f

Decimal floating point

392.65

s

String of characters

“sample”

u

Unsigned integer

x,X

Unsigned hexadecimal

Flags

2a , 2A

description

-

Left-justify within the given field width; Right justification is the default

+

Forces to preceed the result with a plus or minus sign (+ or -) the number with zeroes (0) instead of spaces Left-pads

0

(width)

• • • • • • • • • • • • •

#include <stdio.h> int main() { printf ("Characters: %c %c \n", 'a', 65); printf ("Decimals: %d %ld\n", 1977, 650000); printf ("Preceding with blanks: %10d \n", 1977); printf ("Preceding with zeros: %010d \n", 1977); printf ("Some different radixes: %d %x %#x \n", 100, 100, 100); printf ("floats: %4.2f %E \n", 3.1416, 3.1416); printf ("Width trick: %*d \n", 5, 10); /* This will place 5 spaces thin print 10 */ printf ("%s \n", "A string"); return 0; }

Characters: a A Decimals: 1977 650000 Preceding with blanks: 1977 Preceding with zeros: 0000001977 Some different radixes: 100 64 0x64 floats: 3.14 +3e+000 3.141600E+000 Width trick: 10 A string