diff --git a/calculator.rb b/calculator.rb
new file mode 100644
index 0000000..de9168c
--- /dev/null
+++ b/calculator.rb
@@ -0,0 +1,74 @@
+# checks if user answer is either + or add
+def adding_format()
+  ($answer =~ /[+]/ && $answer.length == 1) || ($answer =~ /[aA][dD][dD]/ && $answer.length == 3)
+end
+
+# checks if user answer is either - or subtract
+def subtracting_format()
+  ($answer =~ /[-]/ && $answer.length == 1) || ($answer =~ /[sS][uU][bB][tT][rR][aA][cC][tT]/ && $answer.length == 8)
+end
+
+# checks if user answer is either * or multiply
+def multiplying_format()
+  ($answer =~ /[*]/ && $answer.length == 1) || ($answer =~ /[mM][uU][lL][tT][iI][pP][lL][yY]/ && $answer.length == 8)
+end
+
+# checks if user answer is either / or divide
+def dividing_format()
+  ($answer =~ /[\/]/ && $answer.length == 1) || ($answer =~ /[dD][iI][vV][iI][dD][eE]/ && $answer.length != 6)
+end
+
+# calculates the first and second number depending on what the operator is
+def calculate(change_operator)
+  print "Enter your first number: "
+  first_num = gets.chomp
+
+  # checks if user only entered in numbers
+  while first_num !~ /\d/
+    print "Numbers only. Try again: "
+    first_num = gets.chomp
+  end
+
+  print "Enter your second number: "
+  sec_num = gets.chomp
+
+  # checks if user only entered in numbers
+  while sec_num !~ /\d/
+    print "Numbers only. Try again: "
+    sec_num = gets.chomp
+  end
+
+  # prompts user to re-enter a number greater than 0 when dividing
+  while (sec_num == 0 && change_operator == "/")
+    print "You can't divide by 0. Try again: "
+    sec_num = gets.chomp
+  end
+
+  # shows result of calculation
+  result = first_num.to_i.send(change_operator, sec_num.to_i)
+  puts "\nResult: #{result}"
+end
+
+# explains to user what they should enter
+puts "Welcome to the Calculator program! Which operator would you like to use?"
+puts "1. add(+) \n2. subtract(-) \n3. multiply(*) \n4. divide(/)"
+print "\nPlease choose one operator (name or sympbol): "
+$answer = gets.chomp
+
+# checks if user entered answer in correct format
+until adding_format() || subtracting_format() || multiplying_format() || dividing_format()
+  print "Incorrect answer. Try again: "
+  $answer = gets.chomp
+end
+
+# asks user to enter first and second number then calculate if
+# the operator they entered is in correct format
+if adding_format()
+  calculate("+")
+elsif subtracting_format()
+  calculate("-")
+elsif multiplying_format()
+  calculate("*")
+elsif dividing_format()
+  calculate("/")
+end