Loops in C (for, while, and do-while)

Loops are used to execute a block of code repeatedly until a specified condition becomes false. C provides three types of loops:

  • for loop
  • while loop
  • do-while loop

1. for Loop

The for loop is used when the number of iterations is known in advance.

Syntax

for (initialization; condition; update)
{
    // statements
}
  • Initialization: Executes only once before the loop starts.
  • Condition: Checked before each iteration.
  • Update: Executes after each iteration.

Example

#include <stdio.h>

int main()
{
    int i;

    for (i = 1; i <= 5; i++)
    {
        printf("%d\n", i);
    }

    return 0;
}

Output

1
2
3
4
5

2. while Loop

The while loop executes a block of code as long as the specified condition is true.

Syntax

while (condition)
{
    // statements
}

Example

#include &lt;stdio.h>

int main()
{
    int i = 1;

    while (i &lt;= 5)
    {
        printf("%d\n", i);
        i++;
    }

    return 0;
}

Output

1
2
3
4
5

3. do-while Loop

The do-while loop executes the loop body at least once, even if the condition is false.

Syntax

do
{
    // statements
} while (condition);

Example

#include &lt;stdio.h>

int main()
{
    int i = 1;

    do
    {
        printf("%d\n", i);
        i++;
    } while (i &lt;= 5);

    return 0;
}

Output

1
2
3
4
5

Example: Sum of First 10 Natural Numbers Using for

#include &lt;stdio.h>

int main()
{
    int i, sum = 0;

    for (i = 1; i &lt;= 10; i++)
    {
        sum += i;
    }

    printf("Sum = %d", sum);

    return 0;
}

Output

Sum = 55

Example: Multiplication Table Using while

#include &lt;stdio.h>

int main()
{
    int num = 5, i = 1;

    while (i &lt;= 10)
    {
        printf("%d x %d = %d\n", num, i, num * i);
        i++;
    }

    return 0;
}

Output

5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50

Example: Menu Using do-while

#include &lt;stdio.h>

int main()
{
    int choice;

    do
    {
        printf("\nMenu\n");
        printf("1. Add\n");
        printf("2. Subtract\n");
        printf("3. Exit\n");
        printf("Enter your choice: ");

        scanf("%d", &amp;choice);

    } while (choice != 3);

    printf("Program Ended.");

    return 0;
}

Difference Between for, while, and do-while

Featurefor Loopwhile Loopdo-while Loop
Condition CheckedBefore executionBefore executionAfter execution
Minimum Executions001
Best Used WhenNumber of iterations is knownNumber of iterations is unknownLoop must execute at least once
Initialization & UpdateIncluded in loop headerWritten separatelyWritten separately

Advantages of Loops

  • Reduce code repetition.
  • Make programs shorter and easier to read.
  • Improve code maintenance.
  • Automate repetitive tasks.

Summary

  • for loop: Best when the number of iterations is known.
  • while loop: Best when the loop depends on a condition and the number of iterations is not fixed.
  • do-while loop: Executes the loop body at least once before checking the condition.
  • Loops are essential for performing repetitive tasks efficiently in C programming.
Category: MCA

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