Variables, Types and Functions

Values and variables

val pi = 3.14        // read-only, cannot be reassigned
var count = 0        // mutable
count = count + 1

val name: String = "Ada"   // explicit type (usually optional)

Prefer val by default and only reach for var when you truly need to reassign — immutable data is easier to reason about.

String templates

Embed values and expressions directly inside strings with $:

val user = "Ada"
val age = 36
println("$user is $age")
println("Next year: ${age + 1}")   // braces for expressions

Functions

Functions are declared with fun. Parameters are name: Type, and the return type follows the parameter list:

fun add(a: Int, b: Int): Int {
    return a + b
}

// single-expression form — type inferred
fun square(n: Int) = n * n

// default and named arguments
fun greet(name: String, greeting: String = "Hello") = "$greeting, $name"
greet("Ada")                       // Hello, Ada
greet("Ada", greeting = "Hi")      // Hi, Ada

Default and named arguments remove the need for the many overloaded methods you often write in Java.

Everything is an expression

if, when and even try return values, so you assign their result directly:

val max = if (a > b) a else b

val label = when (grade) {
    "A", "B" -> "Pass"
    "F"      -> "Fail"
    else     -> "Unknown"
}

Key points

• Use val for read-only, var for mutable; prefer val.
• String templates ($var, ${expr}) replace clumsy concatenation.
• Declare functions with fun; use default and named arguments.
• if and when are expressions that return a value.