Variable declarations

MainActivity

class MainActivity : AppCompatActivity(), View.OnClickListener {
    val TAG_NUMBER = "number"
    val TAG_OPERATOR = "operator"
    val TAG_OPERATION = "operation"

    val OPERATION_DEL = "⌫"
    val OPERATION_CLEAR = "C"
    val OPERATION_EQUALS = "="

    val OPERATOR_ADD = "+"
    val OPERATOR_SUBTRACT = "-"
    val OPERATOR_DIVIDE = "/"
    val OPERATOR_MULTIPLY = "x"
    val OPERATOR_PERCENTAGE = "%"

    var valueOne: Double = Double.NaN
    var valueTwo: Double = 0.0

    var currentAction: String = String()
}