Arithmetic operators in Kotlin - Mini Project: Build & Apply

Arithmetic Operators in Kotlin

📖 Scenario: You are helping a small shop owner calculate prices and discounts for products.

🎯 Goal: Build a Kotlin program that uses arithmetic operators to calculate the total price after discount and tax.

📋 What You'll Learn

Create variables for product price and discount percentage

Create a variable for tax rate

Calculate the discounted price using subtraction and multiplication

Calculate the final price by adding tax

Print the final price

💡 Why This Matters

🌍 Real World

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

💼 Career

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

1

Create product price and discount variables

Create a Double variable called productPrice and set it to 100.0. Create another Double variable called discountPercent and set it to 15.0.

Kotlin

# Your code here

Hint

Use val to create variables and assign the exact values given.

2

Add tax rate variable

Add a Double variable called taxRate and set it to 8.0 to represent 8% tax.

Kotlin

val productPrice: Double = 100.0
val discountPercent: Double = 15.0
# Your code here

Hint

Remember to use val and assign the exact value 8.0.

3

Calculate discounted price and final price

Create a Double variable called discountedPrice that calculates the price after discount using subtraction and multiplication. Then create a Double variable called finalPrice that adds tax to the discounted price using multiplication and addition.

Kotlin

val productPrice: Double = 100.0
val discountPercent: Double = 15.0
val taxRate: Double = 8.0
# Your code here

Hint

Use arithmetic operators -, *, /, and + to calculate prices.

4

Print the final price

Write a println statement to display the finalPrice variable.

Kotlin

val productPrice: Double = 100.0
val discountPercent: Double = 15.0
val taxRate: Double = 8.0
val discountedPrice: Double = productPrice - (productPrice * discountPercent / 100)
val finalPrice: Double = discountedPrice + (discountedPrice * taxRate / 100)
# Your code here

Hint

Use println(finalPrice) to show the result.

Practice

1. Which arithmetic operator in Kotlin is used to find the remainder of a division?

easy

A. The / operator

B. The % operator

C. The * operator

D. The - operator

Solution

1. Step 1: Understand the meaning of each operator

   The % operator gives the remainder after division, / divides, * multiplies, and - subtracts.

2. Step 2: Identify the operator for remainder

   The % operator is specifically for remainder calculation in Kotlin.

3. Final Answer:

   The % operator -> Option B

4. Quick Check:

   Remainder operator = % [OK]

Hint: Remember % means remainder in math and Kotlin [OK]

Common Mistakes:

• Confusing / with %, thinking / gives remainder
• Using * or - for remainder
• Mixing up operators with similar symbols

2. Which of the following is the correct way to write a multiplication operation in Kotlin?

easy

A. val result = 5 x 3

B. val result = 5 . 3

C. val result = 5 / 3

D. val result = 5 * 3

Solution

1. Step 1: Recall Kotlin syntax for multiplication

   Kotlin uses * for multiplication, not x or dot.

2. Step 2: Check each option

   val result = 5 * 3 uses * correctly; others are invalid syntax or different operations.

3. Final Answer:

   val result = 5 * 3 -> Option D

4. Quick Check:

   Multiplication operator = * [OK]

Hint: Use * for multiplication, not x or dot [OK]

Common Mistakes:

• Using x instead of *
• Using dot for multiplication
• Confusing division / with multiplication

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

val a = 10
val b = 3
println(a / b)

medium

A. 3

B. 3.3333333

C. 3.0

D. Error

Solution

1. Step 1: Identify variable types and operation

   a and b are integers, so a / b does integer division.

2. Step 2: Calculate integer division result

   10 divided by 3 is 3.333..., but integer division drops decimals, so result is 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 result with integer division
• Confusing / with floating-point division
• Thinking output is 3.0 or error

4. The following Kotlin code has an error. What is the problem?

val x = 7
val y = 2
val result = x / y.toDouble()
println(result)

medium

A. Cannot call toDouble() on y

B. Division operator / cannot mix Int and Double

C. No error, code runs and prints 3.5

D. Missing explicit type declaration for result

Solution

1. Step 1: Analyze the types involved in division

   y.toDouble() converts y to Double, so x / y.toDouble() divides Int by Double.

2. Step 2: Check Kotlin's handling of mixed numeric types

   Kotlin automatically converts Int to Double for mixed operations, so no error occurs.

3. Final Answer:

   No error, code runs and prints 3.5 -> Option C

4. Quick Check:

   Mixed Int/Double division allowed = 3.5 [OK]

Hint: Kotlin auto-converts Int to Double in mixed division [OK]

Common Mistakes:

• Thinking toDouble() causes error
• Believing mixed types cause syntax error
• Expecting need for explicit type declaration

5. You want to calculate the average of three large integer scores (e.g., 1000000000 each) in Kotlin and get a precise decimal result. Which code snippet correctly does this?

hard

A. val avg = (score1.toDouble() + score2.toDouble() + score3.toDouble()) / 3

B. val avg = (score1 + score2 + score3) / 3.0

C. val avg = (score1 + score2 + score3).toDouble() / 3

D. val avg = (score1 + score2 + score3) / 3

Solution

1. Step 1: Understand integer division problem

   Dividing integers by integer 3 causes integer division, losing decimals.

2. Step 2: Convert all scores to Double before division

   Converting each score to Double ensures floating-point division and precise average.

3. Step 3: Check each option

   val avg = (score1.toDouble() + score2.toDouble() + score3.toDouble()) / 3 converts all scores to Double before adding and dividing, giving correct decimal average.

4. Final Answer:

   val avg = (score1.toDouble() + score2.toDouble() + score3.toDouble()) / 3 -> Option A

5. Quick Check:

   Convert all to Double before division for decimal average [OK]

Hint: Convert all integers to Double before dividing for decimals [OK]

Common Mistakes:

• Dividing integers directly causing integer division
• Converting sum to Double after integer division
• Converting only one score to Double