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

Loops in C programming allow you to execute a block of code multiple times without writing it again and again. They are essential for automation and efficient coding.

In this guide, you will learn for loop, while loop, and do-while loop in C with simple explanations and examples.

What are Loops in C?

Loops are used to repeat a set of instructions until a condition is met.

Benefits:

Reduce code repetition
Save time
Improve efficiency

for Loop in C

The for loop is used when you know how many times you want to run the loop.

Syntax

for (initialization; condition; increment/decrement) {
    // code
}

When to Use for Loop?

Fixed number of iterations
Counting tasks

Types of Loops in C

C provides three types of loops:

Loop Type	Description
for loop	Used when number of iterations is known
while loop	Used when condition-based looping is needed
do-while	Executes at least once

#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;
}