C Loops: for, while, do-while – Complete Guide

Loops in C are used to execute a block of code repeatedly as long as a given condition is true. C supports three primary types of loops:

for loop – when you know how many times to loop
while loop – when you don’t know how many times to loop
do-while loop – when the loop must run at least once

C for Loop

Syntax:

Example:

#include <stdio.h>

int main() {
    for (int i = 1; i <= 5; i++) {
        printf("Count: %d\n", i);
    }
    return 0;
}

Output:

C while Loop

Syntax:

Example:

#include <stdio.h>

int main() {
    int i = 1;
    while (i <= 5) {
        printf("Count: %d\n", i);
        i++;
    }
    return 0;
}

Output:

C do-while Loop

This loop always executes at least once, even if the condition is false on the first check.

Syntax:

Example:

#include <stdio.h>

int main() {
    int i = 1;
    do {
        printf("Count: %d\n", i);
        i++;
    } while (i <= 5);
    return 0;
}

Output:

Loop Comparison Table

Loop Type	Condition Checked	Guaranteed One Execution	Best For
`for`	Before loop	No	Known number of iterations
`while`	Before loop	No	Unknown number, pre-condition
`do-while`	After loop	Yes	At least one execution needed

Best Practices

Tip	Benefit
Avoid infinite loops	Use proper conditions
Use `break` and `continue` wisely	Improve control and logic clarity
Comment complex loops	Improves code readability

Common Mistakes

Mistake	Explanation
Forgetting to update loop counter	Leads to infinite loop
Using `=` instead of `==`	Assignment instead of comparison
Skipping `{}` for multi-line loops	Only the first line is considered

Real-Life Example: Sum of Numbers

#include <stdio.h>

int main() {
    int sum = 0, i = 1;

    while (i <= 100) {
        sum += i;
        i++;
    }

    printf("Sum = %d\n", sum);
    return 0;
}