Kotlin Data Types

Kotlin's Basic Types

Every value in Kotlin has a type, and the compiler uses that type to check which operations are valid. The four types you will use constantly are Int, Double, String, and Boolean, alongside the single-character Char type.

Numbers: Int and Double

fun main() {
    val itemCount: Int = 12
    val unitPrice: Double = 4.99
    val total = itemCount * unitPrice

    println("Total price: $total")
}

Text: String and Char

fun main() {
    val grade: Char = 'A'
    val message: String = "You scored grade $grade"

    println(message)
    println("First character: ${message[0]}")
}

Char values are always wrapped in single quotes and hold exactly one character, while String values use double quotes and can hold any amount of text, including an empty string. Strings in Kotlin are indexed like arrays, so message[0] gives you the first character.

• Byte: 8 bits, range -128 to 127
• Short: 16 bits, range -32768 to 32767
• Int: 32 bits, the default type for whole number literals
• Long: 64 bits, used for very large numbers and must be suffixed with L, e.g. 10000000000L
• Float: 32-bit decimal, suffixed with f
• Double: 64-bit decimal, the default type for decimal literals

fun main() {
    val isActive: Boolean = true
    val age = 30          // inferred as Int
    val weight = 62.5     // inferred as Double

    println("Active: $isActive, Age: $age, Weight: $weight")
    println("age is Int? ${age is Int}")
}