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 out of available options to perform specific operations.

Demo

Prerequisites

Enthusiasm and passion to Learn
Basic knowledge of Ruby language

Solution Steps

The solution I described here is one of the simple solution. I recommend you to first try to write program which is functional and then think of optimization or style improvement later.

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

Let’s first print the menu to the screen to get operation to be performed from user.

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

Next step is to get option from user.
```
operation = gets.to_i
# get option from user and convert into number
```
NOTE: gets will return the data in String format and hence we need to convert it into number explicitly to be used for later purpose.
Now, since we need to accept two numbers from user for each operation, we can define a method as accept_operands at the top of program and then call later whenever it is required.
```
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 return multiple values from Ruby methods.

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

case operation
when 1
  num1, num2 = accept_operands()
  res = num1 + num2
  puts "#{num1} + #{num2} = #{res}"
when 2
  num1, num2 = accept_operands()
  res = num1 - num2
  puts "#{num1} - #{num2} = #{res}"
when 3
  num1, num2 = accept_operands()
  res = num1 * num2
  puts "#{num1} * #{num2} = #{res}"
when 4
  num1, num2 = accept_operands()
  res = num1.to_f / num2
  puts "#{num1} / #{num2} = #{res}"
else
  puts "Invalid choice"
end

Wrap above code in a loop using 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
    num1, num2 = accept_operands()
    res = num1 + num2
    puts "#{num1} + #{num2} = #{res}"
  when 2
    num1, num2 = accept_operands()
    res = num1 - num2
    puts "#{num1} - #{num2} = #{res}"
  when 3
    num1, num2 = accept_operands()
    res = num1 * num2
    puts "#{num1} * #{num2} = #{res}"
  when 4
    num1, num2 = accept_operands()
    res = num1.to_f / num2
    puts "#{num1} / #{num2} = #{res}"
  else
    puts "Invalid choice"
  end

  puts ""   # needed to print next iteration in next line
end

Possible optimizations

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

Share if you Care.