Master C Loops: For, While, and Do‑While Explained with Practical Examples

What Is a Loop in C?

A loop repeats a block of statements until a specified condition becomes false. In C, a loop consists of a body and a control statement that dictates how many times the body executes. Mastering loops is essential for writing efficient and readable C programs.

In this tutorial you’ll discover:

• Definition and purpose of loops in C
• Types of loops: entry‑controlled vs. exit‑controlled
• While loop fundamentals
• Do‑while loop fundamentals
• For loop fundamentals
• Using break and continue
• Choosing the right loop for a given scenario

Types of Loops in C

C loops are classified by the position of their control condition:

• Entry‑controlled loops – the condition is evaluated before the body runs (e.g., while and for).
• Exit‑controlled loops – the condition is evaluated after the body runs (e.g., do‑while).

An infinite loop occurs when the loop never satisfies its termination condition. Common causes include missing a termination check or an always‑true condition.

While Loop in C

The while loop is the simplest form of an entry‑controlled loop. Its syntax is:

while (condition) {
    statements;
}

The condition is evaluated first; if it is true, the body executes. After each execution, the condition is re‑evaluated until it becomes false.

Example – print numbers 1 to 10:

#include <stdio.h>
int main() {
    int num = 1;
    while (num <= 10) {
        printf("%d\n", num);
        num++;
    }
    return 0;
}

Output:

1
2
3
4
5
6
7
8
9
10

Do‑While Loop in C

The do‑while loop guarantees that the body executes at least once, making it an exit‑controlled loop. Syntax:

do {
    statements;
} while (condition);

Example – print the multiplication table of 2 up to 10:

#include <stdio.h>
int main() {
    int num = 1;
    do {
        printf("%d\n", 2 * num);
        num++;
    } while (num <= 10);
    return 0;
}

Output:

2
4
6
8
10
12
14
16
18
20

For Loop in C

The for loop is highly efficient for iterating with a known start, end, and step. Syntax:

for (initialization; condition; increment) {
    statements;
}

• The initialization runs once.
• The condition is checked before each iteration.
• The increment updates the loop variable.

Example – print numbers 1 to 10:

#include <stdio.h>
int main() {
    for (int number = 1; number <= 10; number++) {
        printf("%d\n", number);
    }
    return 0;
}

Output:

1
2
3
4
5
6
7
8
9
10

Complex for loops can include multiple expressions and even empty components:

for (int i = 0, j = num; i < j; i++, j--) {
    // statements
}

Nested loops are common, especially for multidimensional arrays. Example – multiplication tables:

#include <stdio.h>
int main() {
    int i, j;
    int table = 2;
    int max = 5;
    for (i = 1; i <= table; i++) {
        for (j = 0; j <= max; j++) {
            printf("%d x %d = %d\n", i, j, i * j);
        }
        printf("\n");
    }
    return 0;
}

Output:

1 x 0 = 0
1 x 1 = 1
1 x 2 = 2
1 x 3 = 3
1 x 4 = 4
1 x 5 = 5

2 x 0 = 0
2 x 1 = 2
2 x 2 = 4
2 x 3 = 6
2 x 4 = 8
2 x 5 = 10

Break Statement in C

The break keyword exits the nearest enclosing loop or switch statement immediately. Example – stop a while loop when a value reaches 3:

#include <stdio.h>
int main() {
    int num = 5;
    while (num > 0) {
        if (num == 3)
            break;
        printf("%d\n", num);
        num--;
    }
    return 0;
}

Output:

5
4

Continue Statement in C

The continue keyword skips the rest of the current iteration and proceeds to the next loop cycle. Example – skip printing the number 5:

#include <stdio.h>
int main() {
    int nb = 7;
    while (nb > 0) {
        nb--;
        if (nb == 5)
            continue;
        printf("%d\n", nb);
    }
    return 0;
}

Output:

6
4
3
2
1

Choosing the Right Loop

Decide based on when the condition should be evaluated:

• Pre‑test required – use while or for.
• Post‑test required – use do‑while.

Summary

• A loop repeats a block of code until its condition becomes false.
• C offers three primary loops: while, do‑while, and for.
• Entry‑controlled loops evaluate the condition before each iteration; exit‑controlled loops evaluate after.
• Use break to terminate loops early and continue to skip iterations.
• Choose the loop that best matches the control‑flow requirements of your algorithm.