diff --git a/calculator.rb b/calculator.rb
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+# Calculator Project - 8.8.18
+
+# print welcome message and operator options
+puts "Welcome to The Calculator! Which operator would you like to use?"
+puts "1. add(+)"
+puts "2. subtract(-)"
+puts "3. multiply(*)"
+puts "4. divide(/)"
+
+# user input - operation
+puts "Please choose one operator. You can enter the name or the symbol."
+op = gets.chomp
+
+valid_ops = %w[add + subtract - multiply * divide /]
+
+# check for valid user input - operation
+until valid_ops.include?(op)
+  puts "Invalid input."
+  puts "Please choose one operator. You can enter the name or the symbol."
+  op = gets.chomp
+end
+
+# method to verify user input - integer
+def integer?
+  Integer(gets) rescue false
+end
+
+# method to print reprompt message
+def number_reprompt
+  puts "Please enter a valid number."
+end
+
+# user input - first number
+puts "First number:"
+first = integer?
+
+# check for valid user input
+until first
+  number_reprompt
+  first = integer?
+end
+
+# user input - second number
+puts "Second number:"
+second = integer?
+
+# check for valid user input
+until second
+  number_reprompt
+  second = integer?
+end
+
+# operation output
+case op
+
+when "add", "+"
+  puts "#{first} + #{second} = #{first + second}"
+
+when "subtract", "-"
+  puts "#{first} - #{second} = #{first - second}"
+
+when "multiply", "*"
+  puts "#{first} * #{second} = #{first * second}"
+
+when "divide", "/"
+
+  # new input prompt if try to divide by 0
+  while second == 0
+    puts "You cannot divide by zero."
+    puts "Please enter another number."
+    second = integer?
+
+    # check for valid user input
+    until second
+      number_reprompt
+      second = integer?
+    end
+
+  end
+
+  puts "#{first} / #{second} = #{first / second}"
+
+end