While loop execution flow in Java - Mini Project: Build & Apply

While loop execution flow

📖 Scenario: You are helping a cashier count the number of customers entering a store until the store closes.

🎯 Goal: Build a Java program that uses a while loop to count customers until the store closes.

📋 What You'll Learn

Create an integer variable customers starting at 0

Create an integer variable maxCustomers set to 5

Use a while loop with the condition customers < maxCustomers

Inside the loop, increase customers by 1 each time

Print the final number of customers after the loop ends

💡 Why This Matters

🌍 Real World

Counting customers or events until a limit is reached is common in stores, games, or data processing.

💼 Career

Understanding loop execution flow is essential for programming tasks like automation, simulations, and user input handling.

1

Create the initial variable customers

Create an integer variable called customers and set it to 0.

Java

// Your code here

Hint

Use int customers = 0; to create the variable.

2

Add the variable maxCustomers

Add an integer variable called maxCustomers and set it to 5.

Java

public class Main {
    public static void main(String[] args) {
        int customers = 0;
        // Your code here
    }
}

Hint

Use int maxCustomers = 5; to set the limit.

3

Write the while loop to count customers

Write a while loop with the condition customers < maxCustomers. Inside the loop, increase customers by 1 using customers++;.

Java

public class Main {
    public static void main(String[] args) {
        int customers = 0;
        int maxCustomers = 5;
        // Your code here
    }
}

Hint

Use while (customers < maxCustomers) { customers++; } to count customers.

4

Print the final number of customers

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

Java

public class Main {
    public static void main(String[] args) {
        int customers = 0;
        int maxCustomers = 5;
        while (customers < maxCustomers) {
            customers++;
        }
        // Your code here
    }
}

Hint

Use System.out.println(customers); to show the count.

Practice

1. What does a while loop do in Java?

easy

A. Stops the program immediately

B. Executes code only once regardless of condition

C. Runs code only if a condition is false

D. Repeats a block of code as long as a condition is true

Solution

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

   A while loop repeats its code block while the condition remains true.

2. Step 2: Compare options with this behavior

   Only Repeats a block of code as long as a condition is true correctly describes this repeating behavior based on a true condition.

3. Final Answer:

   Repeats a block of code as long as a condition is true -> Option D

4. Quick Check:

   while loop repeats while condition true = A [OK]

Hint: Remember: while loops run only when condition is true [OK]

Common Mistakes:

• Thinking while loop runs once regardless of condition
• Confusing while with if statement
• Believing while loop runs when condition is false

2. Which of the following is the correct syntax to start a while loop in Java?

easy

A. while condition { }

B. while (condition) { }

C. while condition: { }

D. while (condition);

Solution

1. Step 1: Recall Java while loop syntax

   Java requires parentheses around the condition and curly braces for the loop body.

2. Step 2: Check each option

   while (condition) { } matches the correct syntax: while (condition) { }.

3. Final Answer:

   while (condition) { } -> Option B

4. Quick Check:

   Parentheses and braces needed = A [OK]

Hint: Use parentheses for condition and braces for loop body [OK]

Common Mistakes:

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

3. What will be the output of this Java code?

int i = 1;
while (i <= 3) {
  System.out.print(i + " ");
  i++;
}

medium

A. Infinite loop

B. 1 2 3 4

C. 1 2 3

D. 0 1 2 3

Solution

1. Step 1: Analyze the loop condition and variable changes

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

2. Step 2: Trace the output for each iteration

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

3. Final Answer:

   1 2 3 -> Option C

4. Quick Check:

   Prints 1 to 3 with spaces = D [OK]

Hint: Check loop start, end condition, and increments carefully [OK]

Common Mistakes:

• Forgetting i++ causes infinite loop
• Printing extra number after loop ends
• Starting i from 0 instead of 1

4. Identify the error in this code snippet:

int count = 5;
while (count > 0) {
  System.out.println(count);
}

medium

A. No update to count inside the loop causing infinite loop

B. Missing semicolon after while condition

C. Variable count is not initialized

D. Incorrect print statement syntax

Solution

1. Step 1: Check loop condition and variable updates

   The loop condition is count > 0, but count is never changed inside the loop.

2. Step 2: Understand effect of no update

   Without changing count, the loop runs forever, causing an infinite loop.

3. Final Answer:

   No update to count inside the loop causing infinite loop -> Option A

4. Quick Check:

   Loop variable must change to stop loop = B [OK]

Hint: Always update loop variable inside while loop to avoid infinite loops [OK]

Common Mistakes:

• Assuming loop stops without variable update
• Confusing syntax errors with logic errors
• Ignoring infinite loop risks

5. How many times will the loop run in this code?

int x = 10;
while (x > 0) {
  x -= 3;
  System.out.print(x + " ");
}

hard

A. 3 times

B. 5 times

C. 4 times

D. Infinite times

Solution

1. Step 1: Trace the value of x each iteration

   Start x=10. After each loop: x=7, x=4, x=1, x=-2 (loop stops after this).

2. Step 2: Count how many times loop runs

   Loop runs while x > 0, so it runs 3 times before x becomes -2.

3. Final Answer:

   3 times -> Option A

4. Quick Check:

   Subtract 3 until x ≤ 0 = 3 times [OK]

Hint: Count iterations by subtracting until condition fails [OK]

Common Mistakes:

• Counting one less or more iteration
• Ignoring last iteration where x becomes negative
• Assuming infinite loop without checking condition