C while and do…while Loop

In this tutorial, you will learn to create a while and do…while loop in C programming with the help of models.

In programming, loops are used to repeat a block of code until a predetermined condition is met.

C programming has three sorts of loops.

for loop
while loop
do…while loop
In the previous tutorial, we learned about for loop. In this tutorial, we will learn about while and do..while loop.

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while loop

The syntax of the while loop is:

while (testExpression) 
{
    // statements inside the body of the loop 
}

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How while loop functions?

The while loop evaluates the test articulation inside the parenthesis ().

If the test expression is valid, explanations inside the assortment of while loop are executed. Then, the test expression is evaluated again.

The procedure goes on until the test articulation is assessed to bogus.

If the test expression is false, the loop terminates (ends).

To learn more about test expression (when the test expression is evaluated to true and false), check out relational and logical operators.

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Flowchart of while loop

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Example 1: while loop

// Print numbers from 1 to 5

#include <stdio.h>
int main()
{
    int i = 1;
    
    while (i <= 5)
    {
        printf("%d\n", i);
        ++i;
    }

    return 0;
}

Output

1
2
3
4
5

Here, we have initialized i to 1.

When i is 1, the test expression i <= 5 is true. Hence, the body of the while loop is executed. This prints 1 on the screen and the value of i is increased to 2.
Now, i is 2, the test expression i <= 5 is again true. The body of the while loop is executed again. This prints 2 on the screen and the value of i is increased to 3.
This process goes on until i becomes 6. When i is 6, the test expression i <= 5 will be false and the loop terminates.

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do..while loop

The do..while loop is similar to the while loop with one significant distinction. The body of do…while loop is executed at least once. At exactly that point, the test expression is evaluated.

The syntax of the do…while loop is:

do
{
   // statements inside the body of the loop
}
while (testExpression);

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How do…while loop functions?

The body of do..while loop is executed once. At exactly that point, the test expression is evaluated.

If the test expression is valid, the body of the circle is executed again and the test expression is evaluated.

This procedure goes on until the test articulation turns out to be bogus.

If the test expression is false, the loop ends.

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Flowchart of do..while Loop

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Example 2: do..while loop

// Program to add numbers until the user enters zero

#include <stdio.h>
int main()
{
    double number, sum = 0;

    // the body of the loop is executed at least once
    do
    {
        printf("Enter a number: ");
        scanf("%lf", &number);
        sum += number;
    }
    while(number != 0.0);

    printf("Sum = %.2lf",sum);

    return 0;
}

Output

Enter a number: 1.5
Enter a number: 2.4
Enter a number: -3.4
Enter a number: 4.2
Enter a number: 0
Sum = 4.70

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Please feel free to give your comment if you face any difficulty here.

C Flow Control