Function Declare in Kotlin

In Kotlin, you can declare a function using the fun keyword. Here is how you can declare a simple function named printMessage that takes no parameters and returns nothing (i.e., a unit):

fun printMessage() {
    println("Hello, world!")
}

If you want to declare a function that takes parameters, you simply list them inside the parentheses after the function name. Here is an example of a function named sum that takes two integers as parameters and returns their sum:

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

You can also use a shorthand notation for functions that simply return an expression. Here is the same sum function again, but in shorthand notation:

fun sum(a: Int, b: Int) = a + b

Finally, you can declare a function that takes a variable number of arguments using the vararg keyword. Here is an example of a function named sumAll that takes a variable number of integers as parameters and returns their sum:

fun sumAll(vararg numbers: Int): Int {
    var sum = 0
    for (n in numbers) {
        sum += n
    }
    return sum
}

You can now call these functions from within your Kotlin code. For example, to call the printMessage function, you simply write:

printMessage()

And to call the sum function and store the result in a variable named result, you would write something like:

val result = sum(3, 5)