gistfile1.rb

class Expense
    attr_accessor :description, :price
    def initialize(inputted_description, inputted_price)
        # inputted_price is passed as a string, lets
        # convert it to int.

        # price_to_integer has no @ because its just
        # for temporary use, no need to remember it!
        price_to_integer = inputted_price.to_i

        # Assign inputted_description, that is passed
        # in from the constructor, to tne 
        # local attribute @description
        @description = inputted_description

        # Assign price_to_integer, that is passed
        # in from the constructor, to tne 
        # local attribute @price.
        @price = price_to_integer
    end
end

def calculate_total(expense_list)
    total = 0
    # This is a loop in ruby.
    # '.each' assigns each element inside
    # the array to the variable 'expense'
    # in turn.
    expense_list.each do |expense|
        # expense here is an Expense object.
        # so we can use the 'price'
        # and 'desciption' attribute.
        total += expense.price
    end

    # RETURN the value of total. all other
    # variables inside this function will be
    # ignored. we only care about the end result.
    return total
end

def main()

    # This is an ARRAY. Think of it as a list of things
    # in this case we will be using this to store all our expenses.
    all_expenses = []

    puts "Expense manager program starts"
    puts "enter 'EXIT' as a description if you want to sum all expenses"
    loop do

        # Read input from the keyboards. gets()
        # returns a string containing the inputted
        # text
        puts "Put your expense description:"
        inputted_description = gets().chomp()

        # if inputted_description is EXIT, then 'break' the loop.
        # if we don't break, the script will continue forever.
        if inputted_description == 'EXIT'

            # Exits the loop
            break
        end

        puts "Put your expense price:"
        inputted_price = gets().chomp()

        # Now that we have price and description
        # we can create a class INSTANCE.
        # Expense.new calls the constructor, that
        # accepts to arguments
        expense_instance = Expense.new(inputted_description, inputted_price)

        # Put it into the array
        # http://www.ruby-doc.org/core-2.1.2/Array.html#method-i-push
        all_expenses.push(expense_instance)

        # Print how many elements are in the array using count
        # http://www.ruby-doc.org/core-2.1.2/Array.html#method-i-count
        puts "There are now #{all_expenses.count} elements in the list"
    end
    # Out of the loop!
    
    puts "summing up all expenses.."
    # Calling my METHOD. 'calculate_total' returns
    # an integer with the total sum of all expenses
    total_expenses = calculate_total(all_expenses)
    puts "Total expense is: #{total_expenses}"
end

main()