C – while loop in C programming with example

A loop is used for executing a block of statements repeatedly until a given condition returns false. In the previous tutorial we learned for loop. In this guide we will learn while loop in C.

C – while loop

Syntax of while loop:

while (condition test)
{
      //Statements to be executed repeatedly 
      // Increment (++) or Decrement (--) Operation
}

Flow Diagram of while loop

Example of while loop

#include <stdio.h>
int main()
{
   int count=1;
   while (count <= 4)
   {
	printf("%d ", count);
	count++;
   }
   return 0;
}

Output:

1 2 3 4

step1: The variable count is initialized with value 1 and then it has been tested for the condition.
step2: If the condition returns true then the statements inside the body of while loop are executed else control comes out of the loop.
step3: The value of count is incremented using ++ operator then it has been tested again for the loop condition.

Guess the output of this while loop

#include <stdio.h>
int main()
{
     int var=1;
     while (var <=2)
     {
        printf("%d ", var);
     }
}

The program is an example of infinite while loop. Since the value of the variable var is same (there is no ++ or – operator used on this variable, inside the body of loop) the condition var<=2 will be true forever and the loop would never terminate.

Examples of infinite while loop

Example 1:

#include <stdio.h>
int main()
{
     int var = 6;
     while (var >=5)
     {
        printf("%d", var);
        var++;
     }
   return 0;
}

Infinite loop: var will always have value >=5 so the loop would never end.

Example 2:

#include <stdio.h>
int main()
{
    int var =5;
    while (var <=10)
    {
       printf("%d", var);
       var--;
    }
    return 0;
}

Infinite loop: var value will keep decreasing because of –- operator, hence it will always be <= 10.

Use of Logical operators in while loop

Just like relational operators (<, >, >=, <=, ! =, ==), we can also use logical operators in while loop. The following scenarios are valid :

while(num1<=10 && num2<=10)

-using AND(&&) operator, which means both the conditions should be true.

while(num1<=10||num2<=10)

– OR(||) operator, this loop will run until both conditions return false.

while(num1!=num2 &&num1 <=num2)

– Here we are using two logical operators NOT (!) and AND(&&).

while(num1!=10 ||num2>=num1)

Example of while loop using logical operator

In this example we are testing multiple conditions using logical operator inside while loop.

#include <stdio.h>
int main()
{
   int i=1, j=1;
   while (i <= 4 || j <= 3)
   {
	printf("%d %d\n",i, j);
	i++;
	j++;
   }
   return 0;
}

Output:

1 1
2 2
3 3
4 4