Loops & Iteration

Loops allow you to run a block of code repeatedly as long as a specified condition remains true. C offers three loop constructs.

1. The While Loop

Evaluates the condition before executing the loop body. If the condition is false initially, the loop body is never executed:

int i = 1;
while (i <= 5) {
    printf("%d ", i);
    i++; // Don't forget to update loop variable to avoid infinite loops
}
// Output: 1 2 3 4 5

2. The Do-While Loop

Evaluates the condition after executing the loop body. This guarantees that the loop body executes at least once:

#include <stdio.h>

int main() {
    int password_guess;
    int correct_password = 1234;

    do {
        printf("Enter password code: ");
        scanf("%d", &password_guess);
    } while (password_guess != correct_password);

    printf("Access granted.\n");
    return 0;
}

3. The For Loop

A clean, compact loop structure that groups initialization, condition evaluation, and variable update into one line:

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

4. Break and Continue

• break: Terminating statement that immediately exits the loop block.
• continue: Skips the remaining statements in the current iteration and jumps directly to the next condition/iteration update.

for (int i = 1; i <= 6; i++) {
    if (i == 5) {
        break; // Stops loop completely
    }
    if (i % 2 == 0) {
        continue; // Skips printing even numbers
    }
    printf("%d ", i);
}
// Output: 1 3