Difference between While and Do-while Loop in C

This C Tutorial explains the difference between While and Do-while Loop in C Programming.

Do-while Loop in C
In do-while loop, condition is always tested after the execution of the iteration and if condition fails, loop terminates. Therefore, do-while loop executes at least one iteration before termination if condition fails in first iteration!

Do-while loop Syntax:

    /*
     * In do-while: condition is tested in the end of each iteration
     */
 
    do {
        statements;			 
    } while(condition);

The code inside the do {} block will run until the condition inside the while () statement evaluates to false. When the condition is false, the program will exit the do while loop and continue running any code that follows.

Do While Loop Example

#include <stdio.h>
 
int main(void)
{
    int counter = 0;
 
    do {
        /* loop executes just once printing the value 0 */
 
        printf("counter is %d\n", counter);
    } while(counter++ != 0);
 
    return 0;
}

While Loop

In while loop, condition is checked before execution of each iteration and as condition fails, loop terminates.

While Loop Syntax

 
    /*
     * In while, condition is tested in the beginning of each iteration
     */    
 
    while (condition) {                   
        statements;                                   
    }

While Loop Example:

#include <stdio.h>
 
int main(void)
{		
    int counter = 0;
 
    /* loop terminates in the beginning of first iteration */
 
    while (counter++ != 0)
        printf("counter is %d\n", counter);
 
    /* here counter val is printed as 1 */
 
    printf("counter is %d\n", counter);
    return 0;      
}

Difference between While and Do-while Loop in C

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