Loops

Duration: 50 min

Loops allow you to execute a block of code repeatedly. C provides three types of loops: for, while, and do-while. You can also use break and continue to control loop execution.

for Loop

#include <stdio.h>

int main() {
    // Print numbers 1 to 5
    for (int i = 1; i <= 5; i++) {
        printf("%d ", i);
    }
    printf("\n");
    
    // Syntax: for (initialization; condition; increment)
    // initialization: runs once before loop
    // condition: checked before each iteration
    // increment: runs after each iteration
    
    return 0;
}

while Loop

#include <stdio.h>

int main() {
    int i = 1;
    
    while (i <= 5) {
        printf("%d ", i);
        i++;
    }
    printf("\n");
    
    // Useful when you don't know how many iterations needed
    int sum = 0, num = 0;
    while (num < 10) {
        sum += num;
        num++;
    }
    printf("Sum: %d\n", sum);
    
    return 0;
}

do-while Loop

#include <stdio.h>

int main() {
    int i = 1;
    
    // Executes at least once, even if condition is false
    do {
        printf("%d ", i);
        i++;
    } while (i <= 5);
    printf("\n");
    
    // Useful for menu-driven programs
    int choice;
    do {
        printf("Enter 1 to continue, 0 to exit: ");
        scanf("%d", &choice);
    } while (choice != 0);
    
    return 0;
}

break Statement

#include <stdio.h>

int main() {
    // Exit loop when condition is met
    for (int i = 1; i <= 10; i++) {
        if (i == 5) {
            break;  // Exit loop
        }
        printf("%d ", i);
    }
    printf("\n");  // Output: 1 2 3 4
    
    return 0;
}

continue Statement

#include <stdio.h>

int main() {
    // Skip current iteration and go to next
    for (int i = 1; i <= 5; i++) {
        if (i == 3) {
            continue;  // Skip this iteration
        }
        printf("%d ", i);
    }
    printf("\n");  // Output: 1 2 4 5
    
    return 0;
}

Nested Loops

#include <stdio.h>

int main() {
    // Print multiplication table
    for (int i = 1; i <= 3; i++) {
        for (int j = 1; j <= 3; j++) {
            printf("%d ", i * j);
        }
        printf("\n");
    }
    
    // Output:
    // 1 2 3
    // 2 4 6
    // 3 6 9
    
    return 0;
}

Practical Examples

#include <stdio.h>

int main() {
    // Calculate factorial
    int n = 5;
    int factorial = 1;
    for (int i = 1; i <= n; i++) {
        factorial *= i;
    }
    printf("Factorial of %d: %d\n", n, factorial);
    
    // Find sum of digits
    int num = 12345;
    int sum = 0;
    while (num > 0) {
        sum += num % 10;
        num /= 10;
    }
    printf("Sum of digits: %d\n", sum);
    
    return 0;
}

Quiz 1: for Loop

Quiz 2: while Loop

Quiz 3: break Statement

Quiz 4: continue Statement

Quiz 5: Nested Loops