04 Es26 Lab - Program Data And Actions

Program Data and Actions

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Introduction to Programming

Objectives After completing this lesson, you should be able to do the following: • Understand how data are represented in programs • Know how to use the basic input and output functions in a program • Explain how programs are executed in a sequential manner • Use variables in a program • Perform operations on data Introduction to Programming

Program Data and Actions • Every program consists of two components: – A sequence of actions – The data that is acted upon

Introduction to Programming

Simple C Programs Program A

Source code

Output

#include<stdio.h> Hello world. void main(void) { printf(“Hello world.”); }

Program B

#include<stdio.h> void main(void) { printf(“Hello world.\n”); printf(“I’m so happy!”); }

Hello world. I’m so happy!

Introduction to Programming

Sequential Execution Source code

Output

Program C

#include<stdio.h> void main(void) { printf(“Hello world.\n”); printf(“I’m so happy!\n)’ printf(“How about you?”); }

Hello world. I’m so happy! How about you?

Introduction to Programming

Data and Instructions Computer Memory Program Instructions

Data

Introduction to Programming

Variables grade Computer memory

95

int grade; scanf(“%d”, &grade); Introduction to Programming

A Program Using A Variable /* A C program that accepts an integer value and displays it back to the screen */ #include <stdio.h> int main(void) { int grade; printf(“Enter the student’s grade: ”); scanf(“%d”,&grade); printf(“The grade of the student is %d.”, grade); return 0; }

Output Enter the student’s grade: 95 The grade of the student is 95.

Introduction to Programming

Identifiers • Identifiers are used to uniquely reference various objects in a program like variable names, keywords, constants and function names among others • Example: x, y , sum

Introduction to Programming

Identifiers The creation of identifiers are governed by the following rules: 1. It consists only of letters (A-Z, a-z), digits (09) and underscores ( _ ) 2. It cannot start with a digit 3. It does not contain blank spaces

Introduction to Programming

Valid Identifiers • Here are some examples of valid identifiers: x score room201 courseCode TRUE student_number _time Nickname

Introduction to Programming

Identifiers • There is no restriction on the length of an identifier • On some compilers, there is a maximum of 31 characters only • It is also recommended that it is not a redefinition of an identifier in a C standard library such as printf and scanf

Introduction to Programming

C Keywords • • • • • • • • •

auto break case char const continu e default do double

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else enum extern float for goto if int long

• • • • • • • • •

register return short signed sizeof static struct switch typedef

Introduction to Programming

• • • • •

union unsigne d void volatile while

Identifiers • C is a case-sensitive language • In C, even though two identifiers are spelled the same, if the case of each corresponding letter doesn’t match, C regards them as two different names • For example, the identifiers student and Student are considered as two different identifiers

Introduction to Programming

Invalid Identifiers • The following identifiers are invalid: • 1st /* should not start with a digit */ • m&m /* uses illegal character & */ • first year /* space not allowed */

Introduction to Programming

Assignment Statements • A statement that assigns a value to a variable is called an assignment statement and has the format: variable = expression; • For example: x = 100; y = 200; x = y; Introduction to Programming

Swapping Values /* A C program that swaps the values of two variables */ #include <stdio.h> int main(void) { int x, y, temp; printf(“Enter two numbers: ”); scanf(“%d %d”,&x, &y); temp = x; x = y; y = temp; printf(“Value of x: %d\n”, x); printf(“Value of y: %d”, y); return 0; Introduction to Programming }

Performing Calculations on Data /* A C program that adds and subtracts the values of two variables */ #include <stdio.h> int main(void) { int x, y; printf(“Enter two numbers: ”); scanf(“%d %d”,&x, &y); printf(“Sum of %d and %d is %d\n”,x,y,x+y); printf(“Difference of %d and %d is %d”,x,y,x-y); return 0; } Introduction to Programming

Summary • A program consists of instructions and data • The computer executes the instructions in sequential order • A variable stores data such as an integer value • The scanf() function can be used to let a user enter a value for a variable while the printf() function can display the values of variables • The assignment statement can be used to assign a value to a variable specially when performing arithmetic expressions Introduction to Programming