calc

let GetExpression() =
   let priority operator =
      match operator with
      | "+" -> 1
      | "-" -> 1
      | "*" -> 2
      | "/" -> 2
      | "%" -> 2
      | "^" -> 3
      |  _  -> 0

   let isOperator (a : string) = (a.Length = 1 && priority(a) > 0)

   use inputStream = new StreamReader("test.in")
   use outputStream = new StreamWriter("test.out")
   let InStr = inputStream.ReadToEnd()

   let stack = new Stack<string>()

   for i = 0 to InStr.Length - 1 do
      let c = InStr.[i]
      if System.Char.IsDigit(c) then outputStream.WriteLine(c.ToString())
      else
         match c with
         | '(' ->
            stack.push(c.ToString())
         | ')' ->
            while stack.top() <> "(" && (not stack.isEmpty) do
               outputStream.WriteLine(stack.pop())
            ignore(stack.pop())
         | _   ->
            while not stack.isEmpty
               && (priority(stack.top()) >= priority(c.ToString()) && priority(c.ToString()) < 3
               || (priority(stack.top()) >  priority(c.ToString()) && priority(c.ToString()) = 3))
                  do
                     outputStream.WriteLine(stack.pop())
            stack.push(c.ToString())
   while not stack.isEmpty do
      outputStream.WriteLine(stack.pop())