Loop initialization, condition, update in Java - Mini Project: Build & Apply

Loop initialization, condition, update

📖 Scenario: You are helping a small shop owner count the total number of items sold in a day. The shop owner has a list of daily sales numbers for 5 different products.

🎯 Goal: Build a Java program that uses a for loop with proper initialization, condition, and update to sum the total items sold.

📋 What You'll Learn

Create an integer array called sales with exactly these values: 3, 7, 2, 5, 4

Create an integer variable called total and set it to 0

Use a for loop with int i = 0 as initialization, i < sales.length as condition, and i++ as update

Inside the loop, add sales[i] to total

Print the value of total after the loop

💡 Why This Matters

🌍 Real World

Counting totals from lists of numbers is common in stores, inventories, and reports.

💼 Career

Understanding loops and array processing is essential for software development and data handling jobs.

1

Create the sales data array

Create an integer array called sales with these exact values: 3, 7, 2, 5, 4

Java

// Create the sales array with values 3, 7, 2, 5, 4
// Your code here

Hint

Use int[] sales = {3, 7, 2, 5, 4}; to create the array.

2

Initialize the total variable

Create an integer variable called total and set it to 0 inside the main method, below the sales array

Java

public class Main {
    public static void main(String[] args) {
        int[] sales = {3, 7, 2, 5, 4};
        // Create total variable and set to 0
        // Your code here
    }
}

Hint

Write int total = 0; to start counting from zero.

3

Use a for loop to sum sales

Use a for loop with int i = 0 as initialization, i < sales.length as condition, and i++ as update. Inside the loop, add sales[i] to total

Java

public class Main {
    public static void main(String[] args) {
        int[] sales = {3, 7, 2, 5, 4};
        int total = 0;
        // Add a for loop to sum sales into total
        // Your code here
    }
}

Hint

Use for (int i = 0; i < sales.length; i++) and inside add sales[i] to total.

4

Print the total items sold

Write a System.out.println statement to print the value of total after the loop

Java

public class Main {
    public static void main(String[] args) {
        int[] sales = {3, 7, 2, 5, 4};
        int total = 0;
        for (int i = 0; i < sales.length; i++) {
            total += sales[i];
        }
        // Print the total
        // Your code here
    }
}

Hint

Use System.out.println(total); to show the total number of items sold.

Practice

1. Which part of a for loop in Java sets the starting value of the loop variable?

easy

A. Initialization

B. Condition

C. Update

D. Body

Solution

1. Step 1: Understand the parts of a for loop

   A for loop has three parts: initialization, condition, and update.

2. Step 2: Identify the starting value part

   The initialization part sets the starting value of the loop variable before the loop runs.

3. Final Answer:

   Initialization -> Option A

4. Quick Check:

   Starting value = Initialization [OK]

Hint: Initialization always sets the loop's start value [OK]

Common Mistakes:

• Confusing condition with initialization
• Thinking update sets the start value
• Mixing loop body with initialization

2. Which of the following is the correct syntax for a for loop in Java that counts from 0 to 4?

easy

A. for(int i = 0; i < 4; i++) {}

B. for(int i = 0; i <= 4; i++) {}

C. for(int i = 1; i <= 5; i++) {}

D. for(int i = 0; i != 5; i--) {}

Solution

1. Step 1: Check initialization and condition

   for(int i = 0; i <= 4; i++) {} starts at 0 and runs while i is less than or equal to 4, which covers 0 to 4.

2. Step 2: Check update direction

   for(int i = 0; i <= 4; i++) {} increments i by 1 each time, moving forward correctly.

3. Final Answer:

   for(int i = 0; i <= 4; i++) {} -> Option B

4. Quick Check:

   0 to 4 inclusive = for(int i = 0; i <= 4; i++) {} [OK]

Hint: Use i <= max to include last number [OK]

Common Mistakes:

• Using i < 4 excludes 4
• Starting at 1 misses 0
• Decrementing i causes infinite loop

3. What is the output of this Java code?

for(int i = 1; i < 5; i += 2) {
    System.out.print(i + " ");
}

medium

A. 1 2 3 4

B. 1 3 5

C. 2 4

D. 1 3

Solution

1. Step 1: Trace loop values

   i starts at 1, prints 1, then i increases by 2 to 3, prints 3, then i increases by 2 to 5.

2. Step 2: Check loop condition

   Loop runs while i < 5. When i is 5, condition fails, so loop stops.

3. Final Answer:

   1 3 -> Option D

4. Quick Check:

   Prints 1 and 3 only [OK]

Hint: Add update to i and check condition carefully [OK]

Common Mistakes:

• Assuming loop runs when i equals 5
• Forgetting i increments by 2
• Printing values after loop ends

4. Identify the error in this Java loop:

for(int i = 0; i > 5; i++) {
    System.out.println(i);
}

medium

A. Condition causes loop to never run

B. Update should decrement i

C. Initialization is incorrect

D. Missing loop body braces

Solution

1. Step 1: Analyze the loop condition

   The condition is i > 5, but i starts at 0, so 0 > 5 is false immediately.

2. Step 2: Understand loop execution

   Since condition is false at start, loop body never runs.

3. Final Answer:

   Condition causes loop to never run -> Option A

4. Quick Check:

   False condition stops loop immediately [OK]

Hint: Check if condition is true at start to run loop [OK]

Common Mistakes:

• Thinking loop runs at least once
• Confusing > with < in condition
• Assuming update fixes condition

5. You want to print all even numbers from 2 to 20 using a for loop in Java. Which loop correctly does this?

hard

A. for(int i = 2; i < 20; i++) { if(i % 2 == 0) System.out.print(i + " "); }

B. for(int i = 1; i < 20; i++) { if(i % 2 == 0) System.out.print(i + " "); }

C. for(int i = 2; i <= 20; i += 2) { System.out.print(i + " "); }

D. for(int i = 0; i <= 20; i += 2) { System.out.print(i + " "); }

Solution

1. Step 1: Check initialization and update for even numbers

   for(int i = 2; i <= 20; i += 2) { System.out.print(i + " "); } starts at 2 and increments by 2, printing even numbers directly up to 20.

2. Step 2: Verify condition includes 20

   Condition i <= 20 ensures 20 is included in output.

3. Final Answer:

   for(int i = 2; i <= 20; i += 2) { System.out.print(i + " "); } -> Option C

4. Quick Check:

   Start at 2, step 2, up to 20 [OK]

Hint: Start at first even, add 2 each time [OK]

Common Mistakes:

• Starting at 0 prints unwanted 0
• Using < 20 excludes 20
• Forgetting to increment by 2