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Range

Learn ranges with 1..10 and until/downTo.

Range

A range is a sequence of numbers. 1..5 contains all numbers from 1 to 5 (5 inclusive). until excludes the upper bound.

for (i in 1..5) print(i)      // 12345
for (i in 1 until 5) print(i) // 1234
for (i in 5 downTo 1) print(i) // 54321

1..5 includes 5, 1 until 5 does not. downTo counts backward. Ranges are especially useful in for loops.

Two dots (..) make a range; both ends are inclusive.

Practice Count forward and backward

Write a fun main(). Use for (i in 1..5) { println(i) } to count 1 to 5. Then use for (i in 5 downTo 1) { println(i) } to count 5 to 1 backward. Write both loops.

Starter code

Main.kt
fun main() {
    // Count forward and backward
}

Sample solution

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

Expected output

1
2
3
4
5
5
4
3
2
1

Step size

step sets the range's step size. The default step is 1; step 2 jumps by two each time.

for (i in 1..10 step 2) print(i)  // 13579
for (i in 10 downTo 1 step 3) print(i) // 10741

The first loop prints 1, 3, 5, 7, 9. The second counts down from 10 to 1 by threes: 10, 7, 4, 1.

step works with both .. and downTo; the step is always a positive integer.

Questions and answers

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

1 Match the range forms

Term Meaning
1..5 1,2,3,4,5
1 until 5 1,2,3,4
5 downTo 1 5,4,3,2,1
1..1 1

2 Complete the range with until

Question 
for (i in 1 ____ 5) { println(i) }
Answer 
for (i in 1 until 5) { println(i) }

Explanation: The 1 until 5 range gives 1, 2, 3, 4 (5 excluded).

3 Which numbers does 1 until 5 contain?

  • 1,2,3,4,5
  • 5
  • 1,2,3
  • 1,2,3,4 Correct answer

Explanation: until excludes the upper bound: 1, 2, 3, 4.

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