/*
** $Id: rpn.c 739 2008-02-09 00:58:20Z phf $
*/

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <assert.h>

#include "stack.h"

#define SIZE 128

bool is_operator(char c)
{
  return c == '+' || c == '-' || c == '*' || c == '/';
}

void handle_print(void)
{
  if (size() > 0) {
    printf("top: %d\n", top());
  }
  else {
    puts("error: nothing to print since stack is empty");
  }
}

void handle_integer(int i)
{
  if (size() < capacity()) {
    push(i);
  }
  else {
    printf("error: can't push %d since stack is full\n", i);
  }
}

void handle_operator(char c)
{
  if (size() >= 2) {
    int right = top(); pop();
    int left = top(); pop();

    switch (c) {
      case '+':
        push(left+right);
        break;
      case '-':
        push(left-right);
        break;
      case '*':
        push(left*right);
        break;
      case '/':
        push(left/right);
        break;
      default:
        // should be impossible to get here, but we better make sure! :-)
        assert(false);
        break;
    }
  }
  else {
    puts("error: need two values to perform operation");
  }
}

int main()
{
  char buffer[SIZE];

  while (fgets(buffer, SIZE, stdin) != NULL) {
    char op = buffer[0];
    if (op == '.') {
      handle_print();
    }
    else if (is_operator(op)) {
      handle_operator(op);
    }
    else { // assume a string denoting an int
      int value = strtol(buffer, NULL, 10);
      handle_integer(value);
    }    
  }

  return EXIT_SUCCESS;
}