Local variable naming convention

fun fibonacciNumber(index: Int): Long = when(index) {
    0 -> 0
    else -> {
        // does not follow naming conventions: contains underscore symbol (`_`)
        var number_one: Long = 0
        // does not follow naming conventions: starts with an uppercase letter
        var NUMBER_TWO: Long = 1
        // follow naming conventions: starts with a lowercase letter, use camel case and no underscores.
        var numberThree: Long = number_one + NUMBER_TWO

        for(currentIndex in 2..index) {
            numberThree = number_one + NUMBER_TWO
            number_one = NUMBER_TWO
            NUMBER_TWO = numberThree
        }
        numberThree
    }
}