RPN Exercise

RPN Stephen

class RPNCalculator
  def evaluate(expression) # expression = '1 2 +'
    operators = ["+", "-", "*"]
    stack = []
    array = expression.split(" ") # ["1", "2", "+"] 
      array.each do  |i| 
        if operators.include?(i)
          second_operand = stack.pop #is defining a variable that takes the 
          first_operand = stack.pop
          stack.push(first_operand.send(i, second_operand))
          #pushes 1 to stack [1]
          #pushes 2 to stack ["1","2"]
          #pops first second operand our of stack sends to variable
          #pops first operand out of stack and sends to variable
          #pushes first operand 1 sends the operator (+) and then second operand
          #take first operand and sends it a operator and the second operand
      else 
          stack.push(i.to_i) 
        end
    end
    stack.pop
  end
end