Difference between while and do–while in Java - Hands-On Comparison

Difference between while and do-while

📖 Scenario: Imagine you want to ask a user to enter a number until they enter a positive number. You want to see how two different loops behave in this situation.

🎯 Goal: You will create two small Java programs: one using a while loop and one using a do-while loop. You will see how they differ in when they check the condition and how many times the code inside the loop runs.

📋 What You'll Learn

Create a variable to hold a number

Use a while loop to ask for a number until it is positive

Use a do-while loop to ask for a number until it is positive

Print the number entered after each loop

💡 Why This Matters

🌍 Real World

Loops like <code>while</code> and <code>do-while</code> are used in programs to repeat tasks until a condition is met, such as asking a user for input until it is valid.

💼 Career

Understanding loop differences helps in writing efficient and correct code, which is important for software development jobs.

1

Create a variable called number and set it to -1

Create an integer variable called number and set it to -1.

Java

// Create an integer variable called number and set it to -1
// Your code here

Need a hint?

Use int number = -1; to create the variable.

2

Create a boolean variable called isPositive and set it to false

Create a boolean variable called isPositive and set it to false.

Java

int number = -1;
// Create a boolean variable called isPositive and set it to false
// Your code here

Need a hint?

Use boolean isPositive = false; to create the variable.

3

Use a while loop with condition !isPositive to ask for a number and update isPositive

Use a while loop with the condition !isPositive. Inside the loop, set number to 1 (simulating user input) and set isPositive to number > 0.

Java

int number = -1;
boolean isPositive = false;
// Use a while loop with condition !isPositive
// Inside the loop, set number = 1 and isPositive = number > 0
// Your code here

Need a hint?

Use while (!isPositive) { ... } and update variables inside.

4

Print the value of number after the while loop

Write System.out.println(number); to print the value of number after the while loop.

Java

int number = -1;
boolean isPositive = false;
while (!isPositive) {
    number = 1;
    isPositive = number > 0;
}
// Print the value of number
// Your code here

Need a hint?

Use System.out.println(number); to show the number.