While loop in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple while loop

What is the output of this C++ code?

C++

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

A 0 1 2 3

B 2 3 4

C 1 2 3 4

D 1 2 3

💡 Hint

The loop runs while i is less than or equal to 3, starting from 1.

The loop starts with i=1 and prints i, then increments i by 1 each time until i becomes 4, which breaks the loop. So it prints 1 2 3

🧠 Conceptual

intermediate

Understanding while loop condition

What happens if the condition in a while loop is initially false?

A The loop body never runs.

B The loop runs twice.

C The loop runs infinitely.

D The loop body runs once and then stops.

💡 Hint

Think about when the condition is checked in a while loop.

A while loop checks the condition before running the loop body. If the condition is false at the start, the loop body does not run at all.

❓ Predict Output

advanced

Output with nested while loops

What is the output of this C++ code?

C++

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

A 1 1 2 2

B 1 2 2 4

C 1 2 3 4

D 2 4 6 8

💡 Hint

The outer loop runs twice, and for each iteration, the inner loop runs twice.

For i=1, j=1 and 2: prints 1*1=1 and 1*2=2. For i=2, j=1 and 2: prints 2*1=2 and 2*2=4. So output is '1 2 2 4 '.

🔧 Debug

advanced

Identify the error in this while loop

What error does this code produce when compiled and run?

C++

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

A Infinite loop (program never ends)

B Syntax error: missing semicolon

C Runtime error: division by zero

D No output

💡 Hint

Look at how the variable controlling the loop changes inside the loop.

Variable i is never incremented inside the loop, so the condition i < 3 is always true, causing an infinite loop.

🚀 Application

expert

Calculate sum using while loop

What is the value of 'sum' after running this code?

C++

#include <iostream>
int main() {
    int n = 5;
    int sum = 0;
    int i = 1;
    while (i <= n) {
        sum += i;
        i++;
    }
    std::cout << sum;
    return 0;
}

A 5

B 10

C 15

D 0

💡 Hint

Sum of numbers from 1 to 5 is what you need to find.

The loop adds 1 + 2 + 3 + 4 + 5 = 15 to sum.