diff --git a/calculator.rb b/calculator.rb
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+# CALCULATOR EXCERCISE for homework on 02.09.2017
+# Submitted by Tamiko Terada
+
+# METHOD to change a string into a float or integer
+def numberfy(input_string)
+  if input_string.include?(".")
+    input_string.to_f
+  else input_string.to_i
+  end
+end
+
+# METHOD to validate user operator
+def valid_operator(user_operator)
+  possible_operators = [ "add", "+", "subtract", "-", "multiply", "x", "*", "divide", "/" ]
+  possible_operators.include?(user_operator)
+end
+
+# METHOD to calculate values based on allowed operators
+def calculator_method(operator, number_1, number_2)
+  case operator
+  when "add"
+    total = number_1 + number_2
+  when "+"
+    total = number_1 + number_2
+  when "subtract"
+    total = number_1 - number_2
+  when "-"
+    total = number_1 - number_2
+  when "multiply"
+    total = number_1 * number_2
+  when "x"
+    total = number_1 * number_2
+  when "*"
+    total = number_1 * number_2
+  when "divide"
+    total = number_1.to_f / number_2.to_f
+  when "/"
+    total = number_1.to_f / number_2.to_f
+  end
+  return total
+end
+
+# METHOD to check if a string is a valid number
+def can_be_number(string)
+  forced_as_f = string.to_f # force string to be a float
+  forced_as_i = string.to_i # force string to be an integer
+  return string == forced_as_f.to_s || string == forced_as_i.to_s # see if either of the forced strings equal the original
+end
+
+# header
+puts "WELCOME TO CALCULATOR!\n"
+
+# loop for user to terminate the program with "n"
+keep_going = "y"
+until keep_going == "n" do
+  
+  puts " | Display       = | 0 "
+  print " | Enter amount.   | "
+  number_1 = gets.chomp
+  until can_be_number(number_1) do
+    print "~ Enter valid number ~ "
+    number_1 = gets.chomp
+  end
+  number_1 = numberfy(number_1)
+
+  print " | Enter operator. | "
+  operator = gets.chomp
+  until valid_operator(operator) do
+    print "~ Need a valid operator ~ "
+    operator = gets.chomp
+  end
+
+  print " | Enter amount.   | "
+  number_2 = gets.chomp
+  until can_be_number(number_2) do
+    print "~ Need a valid number ~ "
+    number_2 = gets.chomp
+  end
+  number_2 = numberfy(number_2)
+
+  puts "Calculating......... #{number_1} #{operator} #{number_2}"
+  calculated_total = calculator_method(operator, number_1, number_2)
+
+  if calculated_total % 1 == 0
+    puts " | Display       = | #{calculated_total.to_i}"
+  else
+    puts " | Display       = | #{calculated_total}"
+  end
+
+  print "Continue (y/n)? "
+  keep_going = gets.chomp.downcase
+  until keep_going == "y" || keep_going == "n" do
+    print "Please enter 'y' or 'n'!"
+    keep_going = gets.chomp.downcase
+  end
+end
+
+# USER ENTERS CALCULATION ON ONE LINE
+# puts "Enter your expression below."
+# print " | display = | "
+# expression = gets.chomp
+# exp_array = expression.gsub(/\s+/m, ' ').strip.split(" ")
+# until can_be_number(exp_array[0]) && can_be_number(exp_array[-1]) && valid_operator(exp_array[1]) do
+#   expression = gets.chomp
+#   exp_array = expression.gsub(/\s+/m, ' ').strip.split(" ")
+#   exp_array[0] = numberfy(exp_array[0])
+#   exp_array[-1] = numberfy(exp_array[-1])
+# end
+#
+# until (can_be_number("#{exp_array[0]}")) && (can_be_number("#{exp_array[-1]}")) && (valid_operator(exp_array[1]) do
+#   print "Enter a valid expression with spaces! > "
+#   expression = gets.chomp
+#   exp_array = expression.gsub(/\s+/m, ' ').strip.split(" ")
+#   exp_array[0] = numberfy(exp_array[0])
+#   exp_array[-1] = numberfy(exp_array[-1])
+# end