While loop in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5 using a while loop.

C++

#include <iostream>

int main() {
    int i = 1;
    while ([1]) {
        std::cout << i << std::endl;
        i++;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

Ai <= 5

Bi < 1

Ci == 0

Di > 5

Attempts:

3 left

💡 Hint

Common Mistakes

Using a condition that never becomes false, causing an infinite loop.

Using a condition that is false from the start, so the loop never runs.

The condition i <= 5 ensures the loop runs while i is from 1 to 5.

2fill in blank

medium

Complete the code to sum numbers from 1 to 10 using a while loop.

C++

#include <iostream>

int main() {
    int sum = 0;
    int num = 1;
    while ([1]) {
        sum += num;
        num++;
    }
    std::cout << sum << std::endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

Anum < 10

Bnum == 10

Cnum <= 10

Dnum > 10

Attempts:

3 left

💡 Hint

Common Mistakes

Using num < 10 which excludes 10 from the sum.

Using a condition that never ends.

The condition num <= 10 makes sure numbers 1 through 10 are added.

3fill in blank

hard

Fix the error in the while loop condition to count down from 5 to 1.

C++

#include <iostream>

int main() {
    int count = 5;
    while ([1]) {
        std::cout << count << std::endl;
        count--;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

Acount > 5

Bcount >= 1

Ccount == 0

Dcount < 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using a condition that never becomes false.

Using a condition that is false from the start.

The condition count >= 1 keeps the loop running while counting down from 5 to 1.

4fill in blank

hard

Fill both blanks to create a while loop that prints even numbers from 2 to 10.

C++

#include <iostream>

int main() {
    int num = [1];
    while (num [2] 10) {
        std::cout << num << std::endl;
        num += 2;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A2

B<=

C<

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 1 instead of 2.

Using < which excludes 10.

Start at 2 and continue while num is less than or equal to 10 to print even numbers.

5fill in blank

hard

Fill all three blanks to create a while loop that builds a dictionary mapping numbers 1 to 5 to their squares.

C++

#include <iostream>
#include <map>

int main() {
    std::map<int, int> squares;
    int i = [1];
    while (i [2] 5) {
        squares[[3]] = i * i;
        i++;
    }
    for (const auto& [key, value] : squares) {
        std::cout << key << ": " << value << std::endl;
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A1

B<=

Ci

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 0 instead of 1.

Using < which excludes 5.

Using a wrong key for the map.

Start i at 1, loop while i is less than or equal to 5, and use i as the key in the map.

Practice

1.

What does a while loop do in C++?

easy

A. Executes code only once

B. Repeats code a fixed number of times

C. Stops the program immediately

D. Repeats code while a condition is true

Solution

1. Step 1: Understand the purpose of a while loop

   A while loop runs the code inside it repeatedly as long as the condition is true.

2. Step 2: Compare options with definition

   Only Repeats code while a condition is true correctly states this behavior.

3. Final Answer:

   Repeats code while a condition is true -> Option D

4. Quick Check:

   while loop = repeat while true [OK]

Hint: While loops run as long as condition is true [OK]

Common Mistakes:

• Thinking while loops run a fixed number of times
• Confusing while with if statement
• Assuming while loops always run once

2.

Which of the following is the correct syntax for a while loop in C++?

???
{
    // code
}

easy

A. while condition

B. while {condition}

C. while (condition)

D. while: (condition)

Solution

1. Step 1: Recall correct while loop syntax

   The condition must be inside parentheses after the keyword while.

2. Step 2: Check each option

   while (condition) uses while (condition), which is correct syntax in C++.

3. Final Answer:

   while (condition) -> Option C

4. Quick Check:

   while loop syntax = while (condition) [OK]

Hint: Condition in while must be inside parentheses [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using curly braces instead of parentheses
• Adding colon after while

3.

What is the output of this C++ code?

int i = 1;
while (i <= 3) {
    std::cout << i << " ";
    i++;
}

medium

A. 1 2 3 4

B. 1 2 3

C. 0 1 2

D. 3 2 1

Solution

1. Step 1: Analyze loop condition and increments

   Variable i starts at 1 and increases by 1 each loop until i > 3.

2. Step 2: Trace output values

   i = 1 prints "1 ", then 2 prints "2 ", then 3 prints "3 ". Loop stops after i becomes 4.

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   Prints 1 to 3 with spaces [OK]

Hint: Count from start to condition limit inclusive [OK]

Common Mistakes:

• Printing extra number after loop ends
• Starting count from 0 instead of 1
• Printing numbers in reverse

4.

Find the error in this code snippet:

int count = 5;
while (count > 0)
    std::cout << count << " ";

medium

A. Infinite loop because count is never changed

B. Variable count is not declared

C. Syntax error in while condition

D. Missing semicolon after cout statement

Solution

1. Step 1: Check loop body and variable changes

   The loop prints count but does not change it inside the loop.

2. Step 2: Understand loop behavior

   Since count stays 5, condition is always true, causing an infinite loop.

3. Final Answer:

   Infinite loop because count is never changed -> Option A

4. Quick Check:

   Loop variable must change to avoid infinite loop [OK]

Hint: Update loop variable inside while to avoid infinite loop [OK]

Common Mistakes:

• Forgetting to change loop variable
• Assuming loop ends automatically
• Misreading syntax as error

5.

Write a while loop in C++ that prints all even numbers from 2 to 10 inclusive.

Which code snippet correctly does this?

???

hard

A. int n = 2;
while (n <= 10) {
std::cout << n << " ";
n += 2;
}

B. int n = 1;
while (n < 10) {
if (n % 2 == 0) std::cout << n << " ";
n++;
}

C. int n = 2;
while (n < 10) {
std::cout << n << " ";
n += 2;
}

D. int n = 0;
while (n <= 10) {
std::cout << n << " ";
n += 2;
}

Solution

1. Step 1: Understand the requirement

   We need to print even numbers from 2 to 10 inclusive, so numbers: 2,4,6,8,10.

2. Step 2: Check each option

   int n = 2; while (n <= 10) { std::cout << n << " "; n += 2; } starts at 2, increments by 2, and stops at 10 inclusive, printing correct numbers.

3. Final Answer:

   2 4 6 8 10 -> Option A

4. Quick Check:

   Start at 2, add 2 each time, stop at 10 [OK]

Hint: Start at 2, add 2, stop at 10 inclusive [OK]

Common Mistakes:

• Stopping before 10 (using < instead of <=)
• Starting at 1 and missing even numbers
• Including 0 which is not in range