diff --git a/calculator.rb b/calculator.rb
new file mode 100644
index 0000000..615dbf3
--- /dev/null
+++ b/calculator.rb
@@ -0,0 +1,74 @@
+# build a calculator interface that allows the user to input info to perform simple arithmetic.
+# use the input operation and two numbers to provide the results.
+# accept both the name and the symbol for each possible operation. 
+
+puts "\nWelcome to the CALCULATOR program, which operator would you like to use?"
+puts """\nOptions:
+1. add or +
+2. subtract or -
+3. multiply or *
+4. divide or /"""
+
+# handle unexpected input for operations and numbers.
+# optional: add support for handling all cases (uppercase, capitals) for the operations.
+# optional: output a message that informs the user that the input was invalid.
+# optional: asks the user to re-enter the input for the same prompt.
+# optional: does this until the input is valid.
+# optional: uses the newer, valid input.
+
+operations = ["add", "+", "subtract", "-", "multiply", "*", "divide", "/"]
+
+print "\nPlease choose one operator (name or symbol): "
+option =  gets.chomp.downcase
+
+until operations.include?(option)
+  puts "INVALID INPUT, SORRY... Try again.\n"
+  print "\nPlease choose one operator (name or symbol): "
+  option =  gets.chomp.downcase
+end
+
+# handle unexpected input for numbers (expected 0, positive and negative numeric input).
+# Optional: output a message to the command line that informs the user that the input was invalid.
+# Optional: asks the user to re-enter the input for the same prompt.
+# Optional: does this until the input is valid.
+# Optional: uses the newer, valid input.
+
+puts "\nAttention! This CALCULATOR works with two numbers at a time."
+
+print "Please input the FIRST number: "
+num1 = gets.chomp
+while (num1.to_i.to_s != num1.strip)
+  puts "\nINVALID INPUT, SORRY... Try again."
+  print "Please input the FIRST number: "
+  num1 = gets.chomp
+end
+num1 = num1.to_f
+
+print "Please input the SECOND number: "
+num2 = gets.chomp
+while (num2.to_i.to_s != num2.strip)
+  puts "\nINVALID INPUT, SORRY... Try again."
+  print "Please input the SECOND number: "
+  num2 = gets.chomp
+end  
+num2 = num2.to_f
+
+# handle divide when attempting to divide by zero (just exit the program).
+# make your program know when it needs to return an integer versus a float.
+
+if option == "add" || option == "+"
+  puts "\nTOTAL: #{(num1 + num2)}"
+elsif option == "subtract" || option == "-"
+  puts "\nTOTAL: #{(num1 - num2)}"
+elsif option == "multiply" || option == "*"
+  puts "\nTOTAL: #{(num1 * num2)}"
+elsif option == "divide" || option == "/"
+  if num2 == 0 
+    puts "You can't divide by 0. Sorry...\n"
+    exit
+  else  
+    puts "\nTOTAL: #{(num1 / num2)}"
+  end 
+end
+
+puts "\n"