What are the differences between 'val' and 'var' in Kotlin?

val declares an immutable (read-only) reference. After assigning a value to it, you cannot reassign another value.

var declares a mutable reference. Its value can be changed during the variable's lifetime.

Example:

fun main() {
    val readOnlyValue = 10 // Assigned the value 10
    // readOnlyValue = 20 // Compilation error: Val cannot be reassigned

    var mutableValue = 30 // Assigned the value 30
    mutableValue = 40 // Reassigned the value 40
    println(mutableValue) // Will output 40
}

Using val is preferable when possible, as it increases code safety and often makes the code more predictable.