C++ Loop Structure Review Questions

Review C++ loop structures with questions about while loops, loop conditions, counters, increments, repeated statements, and infinite loops.

Section 1: while Loop

1. What is a loop in C++?
2. Why do we use loops instead of writing the same statement repeatedly?
3. What is a while loop in C++? Explain its purpose with an example.
4. What is the syntax of a while loop?
5. How does a while loop work? Explain its execution step by step.
6. What is the difference between a while loop and an if statement?
7. What is an infinite loop? Explain why it occurs in a while loop and write a C++ example.
8. What happens if the condition of a while loop is false at the beginning?
9. Why is initialization important in a while loop?
10. What happens if the loop control variable is not updated?
11. How can you use a while loop to repeatedly take input until the user enters 0?
12. What is the difference between a counter-controlled loop and a sentinel-controlled loop? Give an example of each.
13. Can a while loop execute zero times? Explain with an example.
14. Identify three common mistakes students make when writing while loops and explain how to correct them.

Section 2: do-while Loop

1. What is the difference between a while loop and a do-while loop?
2. Why does a do-while loop execute at least once?
3. Can a do-while loop execute when its condition is initially false? Explain with an example.

Section 3: for Loop

1. What are the three parts of a for loop header?
2. What is the output of for (int i = 1; i <= 3; i++) cout « i « ” “;
3. Why does for (int i = 1; i >= 5; i++) print nothing?
4. What does a semicolon directly after the loop header do?

Section 4: break and continue Loop

1. What is the purpose of the break statement?
2. What is the purpose of the continue statement?
3. What happens when break is executed inside a loop?
4. Does continue terminate a loop?
5. What is the difference between break and continue?
6. Can we use break and continue in a while loop?
7. What happens when continue is used before updating the loop-control variable in a while loop?

Answer:

When continue is used before updating the loop-control variable in a while loop, the update statement may be skipped. As a result, the loop-control variable may never change, causing an infinite loop.

Example:

int i = 1;

while (i <= 5)
{
    if (i == 3)
    {
        continue;
    }

    cout << i << " ";
    i++;
}

Explanation:

• The loop prints 1 and 2.
• When i becomes 3, the continue statement executes.
• The remaining statements, including i++, are skipped.
• The value of i remains 3.
• The loop repeatedly checks the same condition and never terminates.

Correct approach:

int i = 1;

while (i <= 5)
{
    if (i == 3)
    {
        i++;
        continue;
    }

    cout << i << " ";
    i++;
}

Output:

1 2 4 5

Remember: Always ensure that the loop-control variable is updated appropriately before continue in a while loop to avoid an infinite loop.

1. How do break and continue behave in nested loops?