Ruby/ калькулятор через классы и через hash

def say
puts "Enter integer" 
end
# //////////// faktorial
def fakt (b)
     
 
f = b
while b != 1
f*=b-1
b-=1
i = 0
 
end
return f
     end
     
mass = []    
last = 0
opr = ""
      while opr!="exit"
puts"Enter operation (+), (-), (/), (*), (mod), (pow), (sqrt), (sin), (cos), (tg), (ctg), (fakt), (ln), (push), (pop)"    
opr = gets.chomp
 case opr
   when "+"
  say
  int = gets.to_f
  last += int
   when "-"
  say
  int = gets.to_f   
  last -= int
   when "-"
  say
  int = gets.to_f
  last -= int
   when "*"
  say
  int = gets.to_f
  last *= int
   when "/"
      
  say
  int = gets.to_f
  if int == 0
       puts"ERROR"
       else
  last /= int
     end
   when "mod"
  say
  int = gets.to_f
  last = last%int 
   when "pow"
   say
   int = gets.to_f
   last = last**int
   # Unarni
    when "sqrt"
    if last <= 0 
    puts "ERROR"
    else
last = last**0.5
end
    when "sin"
last = Math.sin(last)   
     when "cos"
last = Math.cos(last)   
    when "tg"
last = Math.sin(last)/Math.cos(last)
           when "ctg"
last = Math.cos(last)/Math.sin(last)        
   when "fakt"
   last = fakt(last)
   when "ln"
   last = Math.log(last)  
   
   # work with mass
   when "push"
   say
   int = gets.to_f
   mass.push int 
   last = int
   when "pop"
   mass.pop
   last = mass.pop
   
   
   
 end 
 
 puts "result = #{last}"
 
 puts "  Mass"
 mass << last
 puts mass
 
 
 
      end
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class Operation
 
def plus
 
p "Enter integer +"
@int = gets.chomp.to_i
$last += @int
end
 
def minus
 
p "Enter integer -"
@int = gets.chomp.to_i
$last -= @int
end
end
opr = {"+" => plus, "-" => minus}
a = opr["+"]
$last = 0
while $last != -1
die = Operation.new
puts die.opr["+"]
puts die.minus
 
end

class Calc
  def initialize()
    @accum = 0
  end
 
  def repl
    loop do
      opname = prompt 'Enter one of (+), (-), (exit)'
 
      next if opname.empty?
      break if opname == 'exit'
 
      begin
        op = dispatch opname
        value = prompt('Enter a number').to_f
        op.call value
        puts @accum
      rescue KeyError
        $stderr.puts "Undefined operation: #{opname}"
      end
    end
  rescue Interrupt
    puts
  end
 
  private
  def add(value)
    @accum += value
  end
 
  def subtract(value)
    @accum -= value
  end
 
  OPTABLE = {
    '+' => :add,
    '-' => :subtract
  }
 
  def dispatch(opname)
    method OPTABLE.fetch(opname)
  end
 
  def prompt(msg)
    print "#{msg}> "
    $stdout.flush
    input = gets
    raise Interrupt if input.nil?
    input.strip
  end
end
 
Calc.new.repl