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Array size

Learn array info with size and indices.

Array size

The size of an array is given by the size property. indices gives the range of valid indices (0..size-1), lastIndex gives the last index.

val nums = intArrayOf(3, 7, 2, 5)
println(nums.size)        // 4
println(nums.lastIndex)   // 3
println(nums.indices)     // 0..3

In a 4-element array, size is 4, lastIndex is 3 (since indices start at 0), indices is 0..3. These are useful in loops and bounds checks.

size is a property; no parentheses needed.

Practice Print size and last index

Write a fun main(). Create an array with val nums = intArrayOf(3, 7, 2, 5). Print the size with println(nums.size) and the last index with println(nums.lastIndex).

Starter code

Main.kt
fun main() {
    // Print size and last index
}

Sample solution

Main.kt
fun main() {
    val nums = intArrayOf(3, 7, 2, 5)
    println(nums.size)
    println(nums.lastIndex)
}

Expected output

4
3

Iterating with indices

indices returns a range; it is useful for iterating by index in a for loop.

val nums = intArrayOf(3, 7, 2, 5)
for (i in nums.indices) {
    println(nums[i])
}

This takes each index in turn and accesses the element with nums[i]. indices is the range from 0 to lastIndex.

Index-based iteration is useful when you also need the element's position.

Questions and answers

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

1 Complete the size call

Question 
println(nums.____)
Answer 
println(nums.size)

Explanation: nums.size gives the element count.

2 Match the size properties

Term Meaning
size Element count
lastIndex Last index
indices Index range
0..3 4-element array range

3 In a 4-element array, what is lastIndex?

  • 4
  • 3 Correct answer
  • 0
  • 1

Explanation: Since indices start at 0, the last index is 3.

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