//  MeanvalueIfLet.swift  Copyright (c) Kari Laitinen

//  http://www.naturalprogramming.com

//  2014-09-28  File created.
//  2018-01-02  Last modification.

//  This program demonstrates the if-let construct.

import Foundation

var  number_of_integers_given  =  0
var  sum_of_integers           =  0

print( "\n This program calculates the mean value of"
    +  "\n the integers you enter from the keyboard."
    +  "\n Please, start entering numbers. The program"
    +  "\n stops when you enter a letter. \n" )

var keyboard_input_is_numerical = true

while keyboard_input_is_numerical == true
{
   print( "   Enter an integer: ", terminator: "" )

   // The following if-let construct tests whether the conversion
   // from String to Int is successful.

   if let integer_from_keyboard  =  Int( readLine()! )
   {
      number_of_integers_given  += 1
      sum_of_integers  =  sum_of_integers + integer_from_keyboard
   }
   else
   {
      keyboard_input_is_numerical = false
   }
}

var  mean_value  =  0.0  // The type of mean_value becomes
                         // Double as we assign a Double value

if number_of_integers_given  >  0 
{
   mean_value  =  Double( sum_of_integers ) /
                  Double( number_of_integers_given )
}

print( String( format: "\n The mean value is: %f \n\n", mean_value ) )