Difference between while and do–while in Java - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of while loop with false condition

What is the output of this Java code snippet?

Java

int count = 0;
while (count > 0) {
    System.out.print(count);
    count--;
}
System.out.print("Done");

A Infinite loop

B 0Done

C Compilation error

D Done

💡 Hint

Remember how while loop checks the condition before running the loop body.

The while loop condition is false initially (count=0 > 0 is false), so the loop body never runs. Only "Done" is printed.

❓ Predict Output

intermediate

Output of do-while loop with false condition

What is the output of this Java code snippet?

Java

int count = 0;
do {
    System.out.print(count);
    count--;
} while (count > 0);
System.out.print("Done");

A 0Done

B Done

C Infinite loop

D Compilation error

💡 Hint

Remember how do-while loop runs the body before checking the condition.

The do-while loop runs the body once before checking the condition. It prints 0, then condition is false, then prints "Done".

🧠 Conceptual

advanced

Key difference between while and do-while loops

Which statement best describes the key difference between while and do-while loops in Java?

A while loop checks the condition before running the loop body; do-while loop checks after running the body once.

B while loop runs the body at least once; do-while loop may not run the body at all.

C while loop can only be used with integers; do-while loop can be used with any data type.

D while loop is faster than do-while loop in all cases.

💡 Hint

Think about when the condition is checked in each loop type.

The while loop checks the condition before executing the loop body, so it may not run at all. The do-while loop runs the body once before checking the condition.

🔧 Debug

advanced

Identify the error in this do-while loop

What error will this Java code produce?

Java

int i = 0;
do {
    System.out.println(i);
    i++;
} while (i < 3);

A RuntimeException: infinite loop

B SyntaxError: missing semicolon after i++

C No error, prints 0 1 2

D Compilation error: missing while keyword

💡 Hint

Check punctuation carefully in Java statements.

The statement 'i++' is missing a semicolon at the end, causing a syntax error.

🚀 Application

expert

Number of times loop body executes

Consider this code snippet. How many times will the loop body execute?

Java

int x = 5;
while (x < 5) {
    System.out.println(x);
    x--;
}
do {
    System.out.println(x);
    x--;
} while (x > 0);

A 6 times

B 0 times

C 5 times

D 1 time

💡 Hint

Analyze each loop separately and count executions carefully.

The while loop condition is false initially (5 < 5 is false), so it runs 0 times. The do-while loop runs 5 times, printing 5,4,3,2,1. After printing 1, x becomes 0, and 0 > 0 is false.