Just for fun

brainfuck_interpreter.rb

class BrainfuckInterpreter
  def initialize(program)
    @memory = Array.new(255) { 0 } # 255 memory cells
    @m_ptr = 0                     # memory pointer: which cell
    @i_ptr_stack = Array.new       # instruction pointer stack: used for loops and nested loops
    @i_ptr = 0                     # instruction pointer: which instruction
    @program = program
  end

  def run
    while @program[@i_ptr]
      op = @program[@i_ptr]
      @i_ptr += 1
      
      case op
      when ">" then @m_ptr += 1
      when "<" then @m_ptr -= 1
      when "+" then @memory[@m_ptr] += 1
      when "-" then @memory[@m_ptr] -= 1
      when "." then print @memory[@m_ptr].chr
      when "," then @memory[@m_ptr] = STDIN.getc.ord
      when "[" then @i_ptr_stack << @i_ptr
      when "]" then
        if @memory[@m_ptr] == 0
          @i_ptr_stack.pop
        else
          @i_ptr = @i_ptr_stack.last
        end
      end
    end
  end
end

# program = ",>,>++++++++[<------<------>>-]<<[>[>+>+<<-]>>[<<+>>-]<<<-]>>>++++++[<++++++++>-],<.>." # multiplication: give it two numbers whose multiplied value is less than 10. Input would be "23<Enter>"
# program = ",>++++++[<-------->-],[<+>-]<." # addition: give it two numbers whose added value is less than 10. Input would be "23<Enter>"
program ="++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>." # Hello world!
BrainfuckInterpreter.new(program).run