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Project design

Design the structure of the calculator project and write the skeleton code.

Project: Calculator

In this 5-lesson project you'll build a calculator. Each lesson adds one piece, and by the final lesson you'll have a complete app.

You'll use:

  • fun main() and top-level functions
  • add, subtract, multiply, divide functions
  • if for zero checks
  • try/catch for error handling
  • A for loop for repetition

Ready? Let's start.

File design

We'll put the calculator in a single .kt file. The file holds both the calculation functions and fun main(). The calculation functions are top-level, so they can be called directly as add(5, 3) without creating an object.

Each function returns Int because it produces an integer result. Parameters are also Int.

fun add(a: Int, b: Int): Int {
    return a + b
}

fun main() {
    println(add(5, 3))
}

Practice Write the first skeleton

Write a fun main(). Print Calculator with println.

Sample solution

Main.kt
fun main() {
    println("Calculator")
}

Expected output

Calculator

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What does a calculator do?

  • Saves a file
  • Queries a database
  • Takes two numbers and performs an operation Correct answer
  • Declares a class

Explanation: A calculator takes two numbers and performs an operation.

2 Complete the function signature

Question 
fun add(a: Int, b: Int): ____ { return a + b }
Answer 
fun add(a: Int, b: Int): Int { return a + b }

Explanation: The add function returns Int.

3 Match the project stages

Term Meaning
main Entry point
add Addition
subtract Subtraction
println Output

All lessons in Beginner

1 Kotlin basics

  1. What is Kotlin?
  2. Your first program
  3. The main function
  4. Comments
  5. String templates
  6. Summary - Kotlin basics

2 Variables

  1. val and var
  2. Type inference
  3. const
  4. lateinit
  5. by lazy
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. Boolean and Char
  4. String
  5. Any and Unit
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Elvis operator
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String templates
  3. String methods
  4. substring
  5. split and replace
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. if expression
  4. when
  5. when expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Creating arrays
  2. Array access
  3. Array size
  4. Array loop
  5. Array methods
  6. Summary - Arrays

11 Lists

  1. Creating lists
  2. List operations
  3. List access
  4. List iteration
  5. List methods
  6. Summary - Lists

12 Maps and Sets

  1. Creating sets
  2. Set operations
  3. Creating maps
  4. Map operations
  5. Map iteration
  6. Summary - Maps and Sets

13 Functions

  1. Defining functions
  2. Return values
  3. Expression body
  4. Default parameters
  5. Named arguments
  6. Summary - Functions

14 Null safety

  1. Nullable types
  2. ?, !! and ?:
  3. let
  4. Null check
  5. lateinit
  6. Summary - Null safety

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. Regex
  2. matches and find
  3. replace
  4. StringBuilder
  5. trim and pad
  6. Summary - Advanced strings

17 Enums

  1. enum class
  2. Enum values
  3. Enum properties
  4. when with enum
  5. Enum and range
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. try expression
  5. Custom exceptions
  6. Summary - Exceptions

19 Class basics

  1. class
  2. Constructor
  3. Properties
  4. Methods
  5. this
  6. Summary - Class basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together