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Putting it together

Combine the cart functions with a menu loop.

Putting it together

In the final lesson we combine all pieces: adding items, listing and printing the total. This is the core of a full cart app.

// Add
cart.add(Product("Apple", 5.0))
cart.add(Product("Bread", 3.0))
// List
for (item in cart) {
    println("${item.name}: ${item.price}")
}
// Total
val total = cart.sumOf { it.price }
println("Total: $total")

The output has two parts: the item list and the total. This structure is the core of a real store cart.

Practice Print the total

Add println("Total: $total") after the for loop in the previous cart (two items + for loop). The output: the item list and "Total: 8.0".

Starter code

Main.kt
data class Product(val name: String, val price: Double)

fun main() {
    val cart = mutableListOf<Product>()
    cart.add(Product("Apple", 5.0))
    cart.add(Product("Bread", 3.0))
    val total = cart.sumOf { it.price }
    for (item in cart) {
        println("${item.name}: ${item.price}")
    }
    // Print the total
}

Sample solution

Main.kt
data class Product(val name: String, val price: Double)

fun main() {
    val cart = mutableListOf<Product>()
    cart.add(Product("Apple", 5.0))
    cart.add(Product("Bread", 3.0))
    val total = cart.sumOf { it.price }
    for (item in cart) {
        println("${item.name}: ${item.price}")
    }
    println("Total: $total")
}

Expected output

Apple: 5.0
Bread: 3.0
Total: 8.0

Project complete

Congratulations! You wrote the core of a shopping cart app. You learned:

  • data classes with data class Product
  • mutable lists with mutableListOf
  • adding items with cart.add
  • summing prices with sumOf
  • listing items with for

By combining these, you built the add, list and total logic. Later you can extend the cart with tax, discounts and quantities.

Questions and answers

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

1 Match the integration steps

Term Meaning
cart.add Add item
for (item in cart) List
sumOf Total
println("Total: ...") Print total

2 What does the final version of this project produce?

  • Only the item list
  • Only the total
  • The item list and the total Correct answer
  • Empty output

Explanation: The cart prints both the item list and the total.

3 Complete the total print template

Question 
println("____: $total")
Answer 
println("Total: $total")

Explanation: println("Total: $total") prints the total.

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