Simple Calculator in Ruby

In this tutorial, we are going to see how to build a simple calculator in Ruby.

We will create a menu driven program where we ask user an option from the displayed options shown to perform specific operations.

Demo

Prerequisites

• Enthusiasm and passion to learn
• Basic knowledge of the Ruby language
  • Variables
  • Loop
  • Conditional Operators
  • Getting input from User

Solution Steps

Follow the steps below to build a simple calculator in Ruby.

• Let’s print a menu to the screen to show the available operations to the user.

  puts "--- Calculator ---"
  puts "1. Addition"
  puts "2. Subtraction"
  puts "3. Multiplication"
  puts "4. Division"
  puts "5. Exit"
  

• The next step is to ask the user for an option.

  print "Which operation you want to perform: "
  operation = gets.to_i
  # get option from user and convert into number
  

  NOTE: gets will return the data in as a String, hence we need to convert it into a number.

  • We will need to accept two numbers from the user for each operation. We can define a method as accept_operands at the top of program and then call it later whenever it is needed.

  def accept_operands
    print "Enter first number: "
    operand1 = gets.to_i
    print "Enter second number: "
    operand2 = gets.to_i
    [operand1, operand2]
  end
  

  NOTE: We can only return a single value from a method, and so we choose to return an Array with two elements.

• We need to check the operation option we accepted from the user in the 2nd step and perform the chosen operation:

  case operation
  when 1
    number1, number2 = accept_operands()
    result = number1 + number2
    puts "#{number1} + #{number2} = #{result}"
  when 2
    number1, number2 = accept_operands()
    result = number1 - number2
    puts "#{number1} - #{number2} = #{result}"
  when 3
    number1, number2 = accept_operands()
    result = number1 * number2
    puts "#{number1} * #{number2} = #{result}"
  when 4
    number1, number2 = accept_operands()
    result = number1.to_f / number2
    puts "#{number1} / #{number2} = #{result}"
  else
    puts "Invalid choice"
  end
  

• Wrap the above code in a loop using the loop statement and break out of loop when operation is equal to 5.

  loop do
    # ...
    break if operation == 5
    # ...
  end
  

Solution

# calculator.rb
def accept_operands
  print "Enter first number: "
  operand1 = gets.to_i
  print "Enter second number: "
  operand2 = gets.to_i
  [operand1, operand2]
end

loop do
  puts "--- Calculator ---"
  puts "1. Addition"
  puts "2. Subtraction"
  puts "3. Multiplication"
  puts "4. Division"
  puts "5. Exit"
  print "Which operation you want to perform: "

  operation = gets.to_i
  # get option from user and convert into number

  break if operation == 5

  case operation
  when 1
    number1, number2 = accept_operands()
    result = number1 + number2
    puts "#{number1} + #{number2} = #{result}"
  when 2
    number1, number2 = accept_operands()
    result = number1 - number2
    puts "#{number1} - #{number2} = #{result}"
  when 3
    number1, number2 = accept_operands()
    result = number1 * number2
    puts "#{number1} * #{number2} = #{result}"
  when 4
    number1, number2 = accept_operands()
    result = number1.to_f / number2
    puts "#{number1} / #{number2} = #{result}"
  else
    puts "Invalid choice"
  end

  puts # Will print a newline
end

Possible optimizations

• You can add other mathematical operations.
• We can accept multiple operands in operations like addition.
• We can make it Object Oriented by wrapping the program in a class and use methods as operations name.