calculation.rb

def calculation(first_number, second_number, operator)
  case operator
  when "+"
    result = first_number + second_number
  when "-"
    result = first_number - second_number
  when "*"
    result = first_number * second_number
  when "/"
    result = first_number / second_number.to_f
  end
  result
end

interface.rb

require_relative "calculation"

# Receive two numbers and an operator and return the result
puts "Welcome to the calculator!"

puts "Give me a number"
number1 = gets.chomp.to_i

puts "Give me the operator"
operator = gets.chomp

puts "Give me another number"
number2 = gets.chomp.to_i

# calculation
result = calculation(number1, number2, operator)

# Print the result to the user
puts "Result of #{number1} #{operator} #{number2} is #{result}"