Loops

Introduction

Loops rerun a block — for when you know the trip count, while when you only know the stop condition, do-while when the body must run at least once.

Understanding the topic

for loop Best when iteration count is known.

while loop Condition checked before each iteration.

do-while Body runs once, then condition checked.

• for loop — Best when iteration count is known.
• while loop — Condition checked before each iteration.
• do-while — Body runs once, then condition checked.

Step-by-step explanation

1. for loop — Best when iteration count is known.
2. while loop — Condition checked before each iteration.
3. do-while — Body runs once, then condition checked.

Informative example

Example program:

#include <stdio.h>

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

1 2 3 4 5

Execution workflow

Best practices

• Enable warnings: gcc -Wall -Wextra -std=c11 source.c -o app
• Give every variable a defined value before it is read.
• Stay inside array bounds — C will not stop you from over-running a buffer.

Common mistakes

• Reading uninitialized storage — behavior is undefined.
• Dismissing compiler warnings instead of fixing root causes.
• Ignoring NULL returns from malloc, fopen, and similar APIs.

Hands-on exercise

Practice problems:

• Print multiplication table
• Sum numbers 1 to n
• Nested loops for patterns

Summary

Loops in C — for, while, and do-while iteration patterns.