Decision making using if statement

This tutorial helps beginners to understand, how a variety of if statements help in decision making in c programming. It also contains flow charts and illustrations to improve comprehension

1. Decision Making Using if
Statement
Prepared By:
Dr. Chandan Kumar
Assistant Professor, Computer Science & Engineering Department
Invertis University, Bareilly

2. Decision Making Using if Statement
The statements which are used to take decision
Decision based on some test expression
These statements are used to decide to execute
some code/s and ignore some code/s
Four variant of decision making statement (if)
if statement
if-else statement
nested if statement
else-if statement

3. if statement
This statement is also known as only if
statement or one way branching statement
checks whether the given expression is true of
false
If true then body of the if statement is executed
If false then body of the if statement is ignored
Syntax
if(test_expression)
{
statement/s; // body of if
}

4. Flow Chart if statement

5. Write a C program to print the number entered by user only if the
number entered is even
#include <stdio.h>
#include< conio.h>
void main()
{
int num;
clrscr();
printf(“Enter a number :”);
scanf(“%d”,&num);
if ( num%2==0)
{
printf(“ \nNumber %d is an even number”,num);
}
getch();
}
Output
Enter a number: 2
Number 2 is an even number

6. if-else statement
Also known as two way branching statement
Used when programmer wants to execute
statement/s when the test expression is true
and execute another statement/s if the test
expression is false
Only one block is executed at a time

7. if-else statement
Syntax
if(test_expression)
{
statement/s; // body of if
}
else
{
statement/s; // body of else
}

8. Flow chart if-else

9. Write a C program to print the number entered by user only if the
number entered is even or odd
#include <stdio.h>
#include< conio.h>
void main()
{
int num;
clrscr();
printf(“Enter a number :”);
scanf(“%d”,&num);
if ( num%2==0)
{
printf(“ \nNumber %d is an even number”,num);
}
else
{
printf(“ \nNumber %d is an odd number”,num);
}
getch();
}

10. if-else statement
Output 1
Enter a number: 2
Number 2 is an even number
Output 2
Enter a number: 3
Number 3 is an odd number

11. Nested if statement
An if statement inside another if statement
Programmers used this statement when want to
check one condition inside another condition
When an if else statement is present inside the
body of another “if” or “else”

12. Nested if statement
Syntax
if(test_expression1/ condition 1)
{ //Nested if else inside the body of "if"
if(test_expression2/ condition 2)
{ //Statements inside the body of nested "if”}
else
{ //Statements inside the body of nested "else”}
}
else
{ //Statements inside the body of "else" }

13. Nested if statement

14. Write a C program to print largest number among three numbers
#include<stdio.h>
#include<conio.h>
Void main()
{
int num1,num2,num3;
clrscr();
printf(“Enter three numbers: );
scanf(“%d%d%d”,&num1,&num2,&num3);
if(num1>num2)
{
if(num1>num3)
printf(“ %d is the largest number”,num1);
else
printf(“ %d is the largest number,num3);
}

15. Nested if statement
else
{
if(num2>num3)
printf(“ %d is the largest number”,num2);
else
printf(“ %d is the largest number,num3);
}
getch();
}
Output1:
Enter three numbers: 10 12 11
12 is the largest number

16. else-if statement
Used in program when if statement having
multiple decisions
Syntax
if(test_expression1)
{ //execute code }
.
.
.
else if(test_expression n)
{ //execute code }
else
{ //execute code }

17. else-if statement

18. Write a C program to print largest number among three numbers
#include<stdio.h>
#include<conio.h>
void main()
{
int num1,num2,num3;
clrscr();
printf(“Enter three numbers: );
scanf(“%d%d%d”,&num1,&num2,&num3);
if (num1>num2 && num1>num3)
printf(“ %d is the largest number”,num1);
else if (num2>num1 && num2>num3)
printf(“ %d is the largest number”,num2);
else
printf(“ %d is the largest number”,num3);
getch();
}