for Loop in C Programming

A for loop repeats a block of code while its loop condition remains true. It is especially useful when the initialization, condition and update can be written together.

for Loop Syntax Top ↑

for (initialization; condition; update) {
    // statements repeated by the loop
}

Print 0 to 3 Top ↑

#include <stdio.h>

int main(void) {
    for (int i = 0; i <= 3; i++) {
        printf("%d\n", i);
    }

    return 0;
}

Output

0
1
2
3

The variable i is declared inside the for statement, so its scope is limited to the loop.

break and continue Top ↑

break ends the loop immediately. continue skips the remaining statements in the current iteration and moves to the update step.

#include <stdio.h>

int main(void) {
    for (int i = 1; i <= 5; i++) {
        if (i == 3) {
            break;
        }
        printf("%d\n", i);
    }

    return 0;
}

Output

1
2

Change only break to continue:

#include <stdio.h>

int main(void) {
    for (int i = 1; i <= 5; i++) {
        if (i == 3) {
            continue;
        }
        printf("%d\n", i);
    }

    return 0;
}

Output

1
2
4
5

Change the Step Value Top ↑

#include <stdio.h>

int main(void) {
    for (int i = 0; i <= 25; i += 5) {
        printf("%d\n", i);
    }

    return 0;
}

Output

0
5
10
15
20
25

Nested for Loops Top ↑

#include <stdio.h>

int main(void) {
    for (int row = 1; row <= 3; row++) {
        for (int column = 1; column <= 4; column++) {
            printf("(%d,%d) ", row, column);
        }
        printf("\n");
    }

    return 0;
}

Use different variable names for nested loops so the code is easier to read and the outer-loop value is not hidden.

Reverse a String with a for Loop Top ↑

#include <stdio.h>
#include <string.h>

int main(void) {
    char text[] = "plus2net";
    size_t length = strlen(text);

    for (size_t i = length; i > 0; i--) {
        putchar(text[i - 1]);
    }
    putchar('\n');

    return 0;
}

Output

ten2sulp

Key correction: the last printable character is at length - 1. Starting at length would first access the terminating null character.

Practice with for Loops Top ↑

• Display the numbers from 1 to n.
• Display all even and all odd numbers up to n.
• Find the sum from 1 to n.
• Find the factorial of an input number.
• Display the factors of an input number.
• Reverse the digits of an integer.
• List prime numbers from 1 to n.
• Print lower-case and upper-case ASCII tables.
• Create multiplication tables from 1 to n.

Practice string patterns using for loops

Preserved Example: Value of the Loop Variable After the Loop Top ↑

The original tutorial demonstrated that a loop-control variable declared outside the for statement is still available after the loop and contains the value that caused the loop condition to become false.

#include <stdio.h>

int main(void) {
    int i;

    for (i = 0; i <= 5; i++) {
        printf("i = %d\n", i);
    }

    printf("You came out of the loop.\n");
    printf("i = %d\n", i);
    return 0;
}

Output

i = 0
i = 1
i = 2
i = 3
i = 4
i = 5
You came out of the loop.
i = 6

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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