diff --git a/calculator.rb b/calculator.rb
new file mode 100644
index 0000000..08f07b3
--- /dev/null
+++ b/calculator.rb
@@ -0,0 +1,150 @@
+# calculator.rb
+# https://www.google.com/url?q=https%3A%2F%2Fgithub.com%2FAda-C10%2Fcalculator&sa=D&usd=2&usg=AFQjCNF8YsY1ij6pguWOvbMUgTJO86XQ7Q
+
+$known_adds = ["+", "add", "plus"]
+$known_mins = ["-", "sub", "minus"]
+$known_mults = ["x", "*", "times", "mult"]
+$known_divs = ["/", "÷", "div", "divided by"]
+$known_mods = ["%", "mod", "modulo", "remainder"]
+$known_powers = ["^", "**", "power", "to the power of"]
+$known_operations = $known_adds + $known_mins + $known_mults + $known_divs + $known_mods + $known_powers
+
+def header
+  puts ":" * 50, "\n", "CALCULATOR!", "\n"
+  puts "[Number 1] [Operation] [Number 2] = _______", "\n"
+  puts "You can type any of these operations:"
+  puts $known_adds.join("\t")
+  puts $known_mins.join("\t")
+  puts $known_mults.join("\t")
+  puts $known_divs.join("\t")
+  puts $known_mods.join("\t")
+  puts $known_powers.join("\t")
+  puts "\n"
+end
+
+def footer
+  puts "\n", ":" * 50, "\n"
+end
+
+def add(a,b)
+  $operator_symbol = "+"
+  $result = a+b
+end
+
+def subtract(a,b)
+  $operator_symbol = "-"
+  $result = a-b
+end
+
+def multiply(a,b)
+  $operator_symbol = "x"
+  $result = a*b
+end
+
+def divide(a,b)
+  $operator_symbol = "÷"
+  if b == 0.0
+    $result = nil
+  else
+    $result = a/b
+  end
+end
+
+def remainder(a,b)
+  $operator_symbol = "%"
+  if b == 0.0
+    $result = nil
+  else
+    $result = (a%b).to_i
+  end
+end
+
+def exponify(a,b)
+  $operator_symbol = "^"
+  $result = (a**b)
+end
+
+def reset_errors_hash
+  $errors_hash = Hash.new
+end
+
+def check_number(label)
+  print "Number #{label}\t"
+  number = gets.chomp
+  allowed_number = /\A-{0,1}\d{0,}(\.\d{0,})?\z/
+  if number !~ allowed_number || number == ""
+      $errors_hash["Number #{label}"] = 1
+  else number = number.to_f
+  end
+  return number
+end
+
+def get_math
+  reset_errors_hash
+
+  $num1 = check_number(1)
+
+  print "Operation\t"
+  $operation = gets.chomp
+  unless $known_operations.include?($operation)
+      $errors_hash["THE OPERATION"] = 1
+  end
+
+  $num2 = check_number(2)
+end
+
+def check_math
+  while $errors_hash.has_value?(1)
+    puts "\n", "Oops, try again. I can't accept your input for: #{$errors_hash.keys.join("; ")}.", "\n"
+    get_math
+  end
+end
+
+def do_math(a,b)
+  case
+    when $known_adds.include?($operation)
+      add(a,b)
+    when $known_mins.include?($operation)
+      subtract(a,b)
+    when $known_mults.include?($operation)
+      multiply(a,b)
+    when $known_divs.include?($operation)
+      divide(a,b)
+    when $known_mods.include?($operation)
+      remainder(a,b)
+    when $known_powers.include?($operation)
+      exponify(a,b)
+    else
+      quit("case $operation")
+  end
+  return $result
+end
+
+def print_math(a,b,c,d)
+  if ( c == "÷" || c == "%" ) && b == 0.0
+    puts "\t\tCan't divide by zero! [nil]"
+  else
+    puts "Expression\t#{a} #{c} #{b} = #{$result.round(d)}\t\t(Rounded to up to #{d} decimal places.)"
+  end
+end
+
+def quit(why)
+  puts "Quitting. Something unexpected happened in: #{why}."
+  exit
+end
+
+# here's the program running
+
+header
+get_math
+check_math
+do_math($num1,$num2)
+print_math($num1,$num2,$operator_symbol,5)
+footer
+
+# To do:
+# put arrays in an array of hashes
+# do I really need all of the dollar signs?
+# parentheticals? refactor without asking 3 times. input expression. remove whitespace. split string by a known operator. string 1 = num1, operator = operator, string 2 = num2.
+# square root
+# repeat unless type quit to quit