diff --git a/calculator.rb b/calculator.rb
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--- /dev/null
+++ b/calculator.rb
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+# Calculator Exercise
+# Build a calculator command line interface (CLI) that allows a user to perform simple arithmetic.
+
+# Welcome message:
+puts "\n"
+puts "Welcome to this super basic calculator!"
+puts "\n"
+
+
+
+# Prompt the user for a operation to be made on the calculator:
+print "What operation would you like to do? "
+operation = gets.chomp
+valid_operations = %w[add + addition subtract - subtraction multiply *
+  multiplication divide division / modulo % exponential ^]
+  while !(valid_operations.include?(operation))
+    puts "Input invalid."
+    print "Please enter a basic operation to be made: "
+    operation = gets.chomp
+  end
+
+
+  # Prompt the user for the numbers to be used on the calculation:
+  puts "\n"
+  puts "What are the numbers you would like to perform the operation with?"
+
+  puts "\n"
+  print "Number 1: "
+  first_num = gets.chomp
+  while first_num.match?(/\D/) && !(first_num.match?(/\d\.\d/)) || first_num == ""
+    puts "Input invalid. Please enter a number"
+    print "Number 1: "
+    first_num = gets.chomp
+  end
+  first_num = first_num.to_f
+
+  puts "\n"
+  print "Number 2: "
+  second_num = gets.chomp
+  while second_num.match?(/\D/) && !(second_num.match?(/\d\./)) || second_num == ""
+    puts "Input invalid. Please enter a number"
+    print "Number 1: "
+    second_num = gets.chomp
+  end
+  puts "\n"
+
+
+
+  # Display Integer or Float:
+  print "Would you like to see an integer or a float? "
+  type_answer = gets.chomp.downcase
+  while !(type_answer == "integer" || type_answer== "i" || type_answer == "float" || type_answer == "f")
+    puts "Invalid option."
+    print "Please choose from INTEGER or FLOAT: "
+    type_answer = gets.chomp.downcase
+  end
+  puts "\n"
+
+  if type_answer == "integer"
+    second_num = second_num.to_i
+    first_num = first_num.to_i
+  else
+    second_num = second_num.to_f
+    first_num = first_num.to_f
+  end
+
+
+
+  # Methods for the operations:
+
+  def addition(first_num, second_num)
+    formula = "#{first_num} + #{second_num}"
+    result = first_num + second_num
+    output = [result.round(2), formula]
+    return output
+  end
+
+  def subtraction(first_num, second_num)
+    formula = "#{first_num} - #{second_num}"
+    result = first_num - second_num
+    output = [result.round(2), formula]
+    return output
+  end
+
+  def multiplication(first_num, second_num)
+    formula = "#{first_num} * #{second_num}"
+    result = first_num * second_num
+    output = [result.round(2), formula]
+    return output
+  end
+
+  def division(first_num, second_num)
+    formula = "#{first_num} / #{second_num}"
+    result = first_num / second_num
+    output = [result.round(2), formula]
+    return output
+  end
+
+  def modulo(first_num, second_num)
+    formula = "#{first_num} % #{second_num}"
+    result = first_num % second_num
+    output = [result.round(2), formula]
+    return output
+  end
+
+  def exponential(first_num, second_num)
+    formula = "#{first_num}^#{second_num}"
+    result = first_num ** second_num
+    output = [result.round(2), formula]
+    return output
+  end
+
+
+
+
+  # Conditional + Output
+
+  case operation
+  when "add" , "+"
+    puts "The formula for this operation is: #{addition(first_num, second_num)[1]}"
+    puts "\n"
+    puts "The total of this operation is: #{addition(first_num, second_num)[0]}"
+  when "subtract" , "-"
+    puts "The formula for this operation is: #{subtraction(first_num, second_num)[1]}"
+    puts "\n"
+    puts "The total of this operation is: #{subtraction(first_num, second_num)[0]}"
+  when "multiply", "*"
+    puts "The formula for this operation is: #{multiplication(first_num, second_num)[1]}"
+    puts "\n"
+    puts "The total of this operation is: #{multiplication(first_num, second_num)[0]}"
+  when "divide", "/"
+    if  second_num == 0
+      puts "Cannot perform division with a value <= 0"
+    else
+      puts "The formula for this operation is: #{division(first_num, second_num)[1]}"
+      puts "\n"
+      puts "The total of this operation is: #{division(first_num, second_num)[0]}"
+    end
+  when "modulo", "%"
+    puts "The formula for this operation is: #{modulo(first_num, second_num)[1]}"
+    puts "\n"
+    puts "The total of this operation is: #{modulo(first_num, second_num)[0]}"
+  else #(exponents)
+    puts "The formula for this operation is: #{exponential(first_num, second_num)[1]}"
+    puts "\n"
+    puts "The total of this operation is: #{exponential(first_num, second_num)[0]}"
+  end
+  puts "\n"
+
+
+
+
+  # still needs:
+  # Add support for parentheticals, i.e. 10 / (5 + 5) = 1.