Kotlin: Variable 'result' must be initialized

Question

The compiler is showing error Kotlin: Variable result must be initialized.

Here is the code.

fun main(args: Array<String>) {
    print("Enter two numbers: ")

    // nextDouble() reads the next double from the keyboard
    var first= readLine()!!.toDouble()
    var second = readLine()!!.toInt()

    print("Enter an choice(1-4)): ")
    val operator = readLine()!!.toInt()

    var result: Double

    when (operator) {
        1 -> result = first + second
        2 -> result = first - second
        3 -> result = first * second
        4 -> result = first / second

        else -> {
            println("Error.")
        }
    }

    println("The result is :- " +result)
}

Answer 1

The problem is that when you read the value of result here:

println("The result is :- " +result)

result might not be initialized, because here:

var result: Double

when (operator) {
    1 -> result = first + second
    2 -> result = first - second
    3 -> result = first * second
    4 -> result = first / second

    else -> {
        println("Error.")
    }

You are NOT assigning a value to result in the else branch. You have several options, one could be to make result nullable. For instance:

var result = when (operator) {
    1 -> first + second
    2 -> first - second
    3 -> first * second
    4 -> first / second
    else -> null
}

if (result != null) {
    println("The result is :- " + result)
} else {
    println("Error.")
}

Notice that if the operator is not (1-4) the value of result will be null. Also, in your code you're printing "Error" and then again you're attempting to print the result.

To add something more, you could make the thing a bit nicer if you defined your operator with the when statement as a method reference:

print("Enter an choice(1-4)): ")
val operatorCode = readLine()!!.toInt()

val operator: ((Int) -> Double)? = when (operatorCode) {
    1 -> first::plus
    2 -> first::minus
    3 -> first::times
    4 -> first::div
    else -> null
}

if (operator != null) {
    val result = operator.invoke(second)
    println("The result is :- " + result)
} else {
    println("Error.")
}