Kotlin Syntax

Understanding Kotlin's fundamental syntax rules

📝 Kotlin Syntax Basics

Kotlin syntax is clean, concise, and expressive. Learn the fundamental rules for writing Kotlin code including variables, functions, and basic program structure with practical examples. 


// Basic Kotlin syntax example
fun main() {
    val message = "Learning Kotlin syntax!"
    println(message)
}

Output:

Learning Kotlin syntax!

Basic Syntax Elements

📦

Variables

val (immutable) and var (mutable) 

val name = "John"
var age = 25
⚙️

Functions

Declared with fun keyword 

fun greet(name: String) {
    println("Hello, $name!")
}
🔤

String Templates

Embed expressions in strings 

val result = "2 + 3 = ${2 + 3}"
🎯

Type Inference

Automatic type detection 

val number = 42  // Int
val text = "Hello"  // String

🔹 Variables and Constants

Kotlin uses two keywords for declaring variables: 

// Immutable (read-only) - preferred
val pi = 3.14159
val name = "Kotlin"

// Mutable (can be changed)
var counter = 0
var isActive = true

// Explicit type declaration
val age: Int = 25
var score: Double = 95.5

// Late initialization
lateinit var database: String

Example Usage:

counter = 1 // ✓ Valid (var)
// pi = 3.14 // ✗ Error (val is immutable)

🔹 Functions

Functions are declared using the fun keyword:

🔸 Basic Function Syntax 

// Function with parameters and return type
fun add(a: Int, b: Int): Int {
    return a + b
}

// Single expression function
fun multiply(a: Int, b: Int) = a * b

// Function with default parameters
fun greet(name: String, greeting: String = "Hello") {
    println("$greeting, $name!")
}

// Function with no return value (Unit)
fun printInfo(message: String) {
    println("Info: $message")
}

Usage:

val sum = add(5, 3) // 8
val product = multiply(4, 6) // 24
greet("Alice") // Hello, Alice!
greet("Bob", "Hi") // Hi, Bob!

🔹 String Templates

Kotlin provides powerful string interpolation: 

val name = "Kotlin"
val version = 1.8

// Simple variable interpolation
println("Language: $name")

// Expression interpolation
println("Version: $version")
println("Next version: ${version + 0.1}")

// Complex expressions
val numbers = listOf(1, 2, 3, 4, 5)
println("Sum: ${numbers.sum()}")
println("Average: ${numbers.average()}")

// Multiline strings
val poem = """
    Roses are red,
    Violets are blue,
    Kotlin is awesome,
    And so are you!
""".trimIndent()

Output:

Language: Kotlin
Version: 1.8
Next version: 1.9
Sum: 15
Average: 3.0

🔹 Control Flow

Basic control structures in Kotlin:

🔸 If Expressions 

val score = 85

// Traditional if statement
if (score >= 90) {
    println("Excellent!")
} else if (score >= 70) {
    println("Good job!")
} else {
    println("Keep trying!")
}

// If as expression
val grade = if (score >= 90) "A" 
           else if (score >= 80) "B"
           else if (score >= 70) "C"
           else "F"

println("Grade: $grade")

🔸 When Expression 

val day = 3

val dayName = when (day) {
    1 -> "Monday"
    2 -> "Tuesday"
    3 -> "Wednesday"
    4 -> "Thursday"
    5 -> "Friday"
    6, 7 -> "Weekend"
    else -> "Invalid day"
}

println("Day $day is $dayName")

Output:

Good job!
Grade: B
Day 3 is Wednesday

🔹 Loops

Different ways to iterate in Kotlin: 

// For loop with range
for (i in 1..5) {
    print("$i ")
}
println()

// For loop with list
val fruits = listOf("apple", "banana", "orange")
for (fruit in fruits) {
    println("I like $fruit")
}

// While loop
var count = 3
while (count > 0) {
    println("Countdown: $count")
    count--
}

// Repeat function
repeat(3) {
    println("Kotlin is fun!")
}

Output:

1 2 3 4 5
I like apple
I like banana
I like orange
Countdown: 3
Countdown: 2
Countdown: 1
Kotlin is fun!
Kotlin is fun!
Kotlin is fun!

🧠 Test Your Knowledge

Which keyword is used to declare functions in Kotlin?