Arithmetic operators in Java - Mini Project: Build & Apply

Arithmetic Operators in Java

📖 Scenario: You are helping a small shop owner calculate the total cost of items bought by customers. You will use arithmetic operators to add, subtract, multiply, and divide prices.

🎯 Goal: Build a simple Java program that uses arithmetic operators to calculate the total price, discount, and final amount to pay.

📋 What You'll Learn

Create variables for item prices

Create a variable for discount percentage

Calculate total price using addition

Calculate discount amount using multiplication

Calculate final price after discount using subtraction

Print the final price

💡 Why This Matters

🌍 Real World

Calculating prices and discounts is common in shopping and billing systems.

💼 Career

Understanding arithmetic operators is essential for any programming job involving calculations or data processing.

1

Create item price variables

Create three double variables called price1, price2, and price3 with values 10.5, 20.0, and 5.5 respectively.

Java

# Your code here

Hint

Use double type for prices and assign the exact values.

2

Add discount percentage variable

Add a double variable called discountPercent and set it to 10.0 to represent a 10% discount.

Java

public class ArithmeticOperators {
    public static void main(String[] args) {
        double price1 = 10.5;
        double price2 = 20.0;
        double price3 = 5.5;
        // Your code here
    }
}

Hint

Remember to use double for the discount percentage.

3

Calculate total, discount amount, and final price

Calculate the total price by adding price1, price2, and price3 into a double variable called totalPrice. Then calculate the discount amount by multiplying totalPrice with discountPercent divided by 100 into a double variable called discountAmount. Finally, calculate the final price after discount by subtracting discountAmount from totalPrice into a double variable called finalPrice.

Java

public class ArithmeticOperators {
    public static void main(String[] args) {
        double price1 = 10.5;
        double price2 = 20.0;
        double price3 = 5.5;
        double discountPercent = 10.0;
        // Calculate totalPrice, discountAmount, and finalPrice
        // Your code here
    }
}

Hint

Use + for addition, * for multiplication, and - for subtraction.

4

Print the final price

Use System.out.println to print the text "Final price: " followed by the value of finalPrice.

Java

public class ArithmeticOperators {
    public static void main(String[] args) {
        double price1 = 10.5;
        double price2 = 20.0;
        double price3 = 5.5;
        double discountPercent = 10.0;
        double totalPrice = price1 + price2 + price3;
        double discountAmount = totalPrice * discountPercent / 100;
        double finalPrice = totalPrice - discountAmount;
        // Print the final price
        // Your code here
    }
}

Hint

Use System.out.println("Final price: " + finalPrice); to print the result.

Practice

1. Which of the following is the correct symbol for the modulus operator in Java, which gives the remainder of a division?

easy

A. *

B. /

C. -

D. %

Solution

1. Step 1: Understand the modulus operator

   The modulus operator returns the remainder after division of two numbers.

2. Step 2: Identify the correct symbol in Java

   In Java, the symbol for modulus is %.

3. Final Answer:

   % -> Option D

4. Quick Check:

   Modulus operator = % [OK]

Hint: Modulus operator is always % in Java math [OK]

Common Mistakes:

• Confusing modulus % with division /
• Using * or - instead of %
• Thinking modulus returns quotient

2. Which of the following Java statements correctly calculates the product of two integers a and b?

easy

A. int result = a / b;

B. int result = a + b;

C. int result = a * b;

D. int result = a % b;

Solution

1. Step 1: Identify the multiplication operator

   In Java, the multiplication operator is *.

2. Step 2: Check the statement that uses multiplication

   The statement int result = a * b; correctly multiplies a and b.

3. Final Answer:

   int result = a * b; -> Option C

4. Quick Check:

   Multiplication operator = * [OK]

Hint: Use * for multiplication in Java expressions [OK]

Common Mistakes:

• Using + instead of * for multiplication
• Confusing division / with multiplication
• Using % which is remainder, not product

3. What is the output of the following Java code?

int x = 10;
int y = 3;
System.out.println(x / y);

medium

A. 3

B. 3.3333333

C. 3.0

D. 4

Solution

1. Step 1: Understand integer division in Java

   Both x and y are integers, so division drops the decimal part.

2. Step 2: Calculate integer division result

   10 divided by 3 is 3.333..., but integer division returns 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Integer division drops decimals = 3 [OK]

Hint: Integer division drops decimals, result is integer [OK]

Common Mistakes:

• Expecting decimal output with int division
• Confusing / with % operator
• Assuming automatic float conversion

4. Identify the error in the following Java code snippet:

int a = 5;
int b = 0;
int c = a / b;
System.out.println(c);

medium

A. Division by zero causes runtime error

B. Variable c is not declared

C. Missing semicolon after declaration

D. Incorrect use of modulus operator

Solution

1. Step 1: Analyze the division operation

   The code divides a by b, where b is zero.

2. Step 2: Understand division by zero in Java

   Dividing an integer by zero causes a runtime ArithmeticException error.

3. Final Answer:

   Division by zero causes runtime error -> Option A

4. Quick Check:

   Division by zero throws error [OK]

Hint: Never divide by zero; it crashes the program [OK]

Common Mistakes:

• Ignoring division by zero error
• Thinking it returns zero or infinity
• Confusing syntax error with runtime error

5. Given the code below, what will be the value of result after execution?

int a = 15;
int b = 4;
int result = a / b + a % b * 2;

hard

A. 11

B. 9

C. 8

D. 7

Solution

1. Step 1: Calculate integer division and modulus

   15 / 4 = 3 (integer division), 15 % 4 = 3 (remainder).

2. Step 2: Apply operator precedence and compute expression

   Expression is 3 + 3 * 2. Multiplication first: 3 * 2 = 6. Then addition: 3 + 6 = 9.

3. Step 3: Re-check calculation

   Wait, re-check: 15 / 4 = 3, 15 % 4 = 3, 3 * 2 = 6, 3 + 6 = 9.

4. Final Answer:

   9 -> Option B

5. Quick Check:

   Division + (modulus * 2) = 9 [OK]

Hint: Remember * before + in mixed expressions [OK]

Common Mistakes:

• Adding before multiplying
• Confusing division and modulus results
• Forgetting integer division truncates decimals