diff --git a/calculator.rb b/calculator.rb
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+++ b/calculator.rb
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+# Calculator.rb assignment
+
+# array of arrays 
+operators = [
+  ["add", "+"], 
+  ["subtract", "-"], 
+  ["multiply", "*"], 
+  ["divide", "/"]
+]
+
+# added this operator_check long array to ensure user's input is only valid if on this list
+operators_check = 
+  ["add", "+", 
+  "subtract", "-", 
+  "multiply", "*", 
+  "divide", "/"]
+
+# only accept digits as input
+def is_number(string)
+  if string.length == 0
+    return false
+  end
+  return string.scan(/\D/).empty?
+end
+
+# welcome user to program, provide list of oeprators, looping through list options
+puts "Welcome to the Calculator program! I hear you need help..."
+puts "Which operator would you like to use from the below list?"
+4.times do |i|
+  puts "#{i+1}: #{operators[i][0]} (#{operators[i][1]})"
+end
+
+# get user's operator pick and reinstate. Throw error if selection is not on offered list
+puts "Enter your chosen operator now (name or symbol)."
+operator_pick = gets.chomp
+# use method.include to throw error if user input is not on the operator list and prompt user to try again
+until operators_check.include?(operator_pick)
+  puts "ERROR: invalid entry. Please select operator from list."
+  puts "Enter your chosen operator now (name or symbol)."
+  operator_pick = gets.chomp
+  puts "You've selected the #{operator_pick} operator."
+end
+
+# get user's first number and reinstate. Error if less than 0
+# initially used .to_i on gets.chomp but this converted string to 0
+# instead, check if num_one_pick is a number, before calling to_i. If not a number, throw error
+# include .to_f to handle float entries as well (but now all outputs are floats? hm)
+puts "Next: select a number for this math operation."
+num_one_pick = gets.chomp
+while is_number(num_one_pick) == false
+  puts "ERROR: this entry is not valid."
+  puts "Next: select a number for this math operation."
+  num_one_pick = gets.chomp
+end
+num_one_pick = num_one_pick.to_i.to_f
+
+puts "You've selected #{num_one_pick} as your first number."
+puts "#{num_one_pick} is a great number."
+
+# get user's second number and reinstate. Error if less than 0
+# ensure user input is numerical and reject if non-numerical
+# if operator chosen is division, (to prevent division by 0) throw error, prompting the user to enter another number
+puts "Finally: select your second number for the Calculator."
+num_two_pick = gets.chomp
+while is_number(num_two_pick) == false || (num_two_pick == "0" && (operator_pick == "divide" || operator_pick == "/"))
+  puts "ERROR: this entry is not valid."
+  puts "Please enter a different number for the Calculator."
+  num_two_pick = gets.chomp
+end
+
+num_two_pick = num_two_pick.to_i.to_f
+
+puts "You've selected #{num_two_pick} as your second number."
+puts "#{num_two_pick} is also a great number."
+
+# wrap up and reinstate equation, along with solution
+puts "You have created the following problem: #{num_one_pick} #{operator_pick} #{num_two_pick}"
+puts "The solution to your problem is: "
+
+# use case command to complete equation
+case operator_pick
+  when "add", "+"
+puts (num_one_pick + num_two_pick)
+  when "subtract", "-"
+puts (num_one_pick - num_two_pick)
+  when "multiply", "*"
+puts (num_one_pick * num_two_pick)
+  when "divide", "/"
+puts (num_one_pick / num_two_pick)
+end 
+puts "Thank you for using The Calculator. Come back next time you need help!"