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The for loop

Learn to write counted loops with for.

The for loop

The for loop runs a block multiple times. In Kotlin, for iterates over a range or a collection.

for (i in 1..5) {
    println(i)
}

This runs the block for each value of i from 1 to 5 (5 inclusive), printing 1, 2, 3, 4, 5. 1..5 is a range; you'll see it in detail later.

i is the loop variable and takes the next value each step. The loop ends when the range is exhausted.

for over a collection

for can also iterate over the items of a collection (for example, a list).

val fruits = listOf("apple", "pear", "cherry")
for (fruit in fruits) {
    println(fruit)
}

Here fruit takes one item from the list each step: first "apple", then "pear", then "cherry". You'll learn listOf later.

You don't need to write the loop variable's type; Kotlin infers it.

Practice Print 1 to 5

Write a fun main(). Use a for (i in 1..5) loop to call println(i). The output should be 1, 2, 3, 4, 5, each on its own line.

Starter code

Main.kt
fun main() {
    // Print 1 to 5
}

Sample solution

Main.kt
fun main() {
    for (i in 1..5) {
        println(i)
    }
}

Expected output

1
2
3
4
5

Questions and answers

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

1 How many lines does for (i in 1..3) { println(i) } print?

  • 3 lines Correct answer
  • 2 lines
  • 4 lines
  • 1 line

Explanation: The 1..3 range has 3 values: 1, 2, 3.

2 Complete the for range

Question 
for (i in 1____5) { println(i) }
Answer 
for (i in 1..5) { println(i) }

Explanation: The 1..5 range counts from 1 to 5 (5 inclusive).

3 Match the for forms

Term Meaning
for (i in 1..5) Range loop
for (item in list) List loop
1..5 Range
i Loop variable

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