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The if statement

Learn how to check a condition with if.

The if statement

The if statement runs a block when a condition is true. The condition goes in parentheses; the block is wrapped in curly braces.

val age = 18
if (age >= 18) {
    println("Adult")
}

The condition is a Boolean expression: true or false. If true, the block runs; if false, it is skipped. Comparison operators (>, <, ==, >=, <=) were covered earlier.

For single-line blocks the braces are optional, but recommended for readability.

Comparison and logical operators

Conditions use comparison operators. These were covered earlier but let's quickly recap.

5 > 3       // true
5 < 3       // false
5 == 5      // true
5 != 3      // true
5 >= 5      // true
5 <= 4      // false

== checks value equality, != checks inequality. For Strings, == compares content too (unlike Java).

Logical operators && (and), || (or), ! (not) combine conditions: age >= 18 && age < 65.

Practice Check the age

Write a fun main(). Assign 20 to val age. Use if (age >= 18) to print println("Adult").

Starter code

Main.kt
fun main() {
    // Check the age
}

Sample solution

Main.kt
fun main() {
    val age = 20
    if (age >= 18) {
        println("Adult")
    }
}

Expected output

Adult

Questions and answers

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

1 When does if (age >= 18) run?

  • When age is below 18
  • When age is 18 or above Correct answer
  • Always
  • Never

Explanation: >= 18 covers 18 and above.

2 Complete the comparison operator

Question 
val adult = age ____ 18
Answer 
val adult = age >= 18

Explanation: age >= 18 treats 18 and above as adult.

3 Match the conditions

Term Meaning
age >= 18 18 or above
age < 18 Below 18
age == 18 Exactly 18
age != 18 Not 18

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