Why loops are needed in C++ - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple for loop

What is the output of this C++ code snippet?

C++

#include <iostream>
int main() {
    for (int i = 1; i <= 3; i++) {
        std::cout << i << " ";
    }
    return 0;
}

A 1 2 3

B 0 1 2 3

C 1 2 3 4

D 3 2 1

💡 Hint

The loop starts at 1 and runs while i is less than or equal to 3.

The loop variable i starts at 1 and increments by 1 each time until it reaches 3, printing each value followed by a space.

🧠 Conceptual

intermediate

Why use loops instead of repeated code?

Why are loops useful in programming compared to writing the same code multiple times?

A Loops increase the size of the program by duplicating code.

B Loops reduce code repetition and make programs shorter and easier to maintain.

C Loops are only used to confuse beginners and have no real benefit.

D Loops make programs run slower by repeating code unnecessarily.

💡 Hint

Think about how many times you want to do the same task.

Loops let you write a task once and repeat it many times, which saves time and reduces mistakes.

❓ Predict Output

advanced

Output of nested loops

What is the output of this nested loop code?

C++

#include <iostream>
int main() {
    for (int i = 1; i <= 2; i++) {
        for (int j = 1; j <= 2; j++) {
            std::cout << i << j << " ";
        }
    }
    return 0;
}

A 11 21 12 22

B 21 22 11 12

C 12 11 22 21

D 11 12 21 22

💡 Hint

The outer loop controls the first digit, the inner loop controls the second digit.

The outer loop runs i=1 then i=2. For each i, the inner loop runs j=1 and j=2, printing i and j together.

🔧 Debug

advanced

Identify the error in this loop

What error will this code produce when compiled or run?

C++

#include <iostream>
int main() {
    for (int i = 0; i < 5; i++)
        std::cout << i << std::endl;
    std::cout << j;
    return 0;
}

A Compilation error: 'j' was not declared in this scope

B Runtime error: division by zero

C No error, prints numbers 0 to 4 and then 0

D Compilation error: missing semicolon after for loop

💡 Hint

Check if all variables used are declared.

Variable 'j' is used but never declared, causing a compilation error.

🚀 Application

expert

Count how many times a loop runs

How many times will the loop body execute in this code?

C++

#include <iostream>
int main() {
    int count = 0;
    for (int i = 10; i > 0; i -= 3) {
        count++;
    }
    std::cout << count;
    return 0;
}

A 5

B 3

C 4

D 6

💡 Hint

Start from 10 and subtract 3 each time until i is no longer greater than 0.

The loop runs while i is 10, 7, 4, 1 (4 times). When i becomes -2, loop stops.