//-----------------------------------------------------------
//  Purpose:    Implementation of postfix calculator
//  Author:     John Gauch
//-----------------------------------------------------------
#include "stack5/stack5.h"
#include <cstdlib> 
#include <string>
using namespace std;

//-----------------------------------------------------------
// Use stack to evaluate postfix expressions
//-----------------------------------------------------------
int evaluate()
{
   Stack stack;
   string str;
   double num1, num2, res;

   cout << "Enter postfix expression: ";
   cin >> str;
   while (str != "=")
   {
      // Push number on stack
      if ((str[0] >= '0') && (str[0] <= '9'))
      {
	 stack.Push(atof(str.c_str()));
      }

      // Handle addition
      else if (str == "+")
      {
	 if (stack.GetLength() < 2)
	 {
	    cout << "Error: Not enough data for '" << str << "' operation\n";
	    return -1;
	 }
	 stack.Pop(num2);
	 stack.Pop(num1);
	 stack.Push(num1 + num2);
      }

      // Handle subtraction
      else if (str == "-")
      {
	 if (stack.GetLength() < 2)
	 {
	    cout << "Error: Not enough data for '" << str << "' operation\n";
	    return -1;
	 }
	 stack.Pop(num2);
	 stack.Pop(num1);
	 stack.Push(num1 - num2);
      }

      // Handle multiplication
      else if (str == "*")
      {
	 if (stack.GetLength() < 2)
	 {
	    cout << "Error: Not enough data for '" << str << "' operation\n";
	    return -1;
	 }
	 stack.Pop(num2);
	 stack.Pop(num1);
	 stack.Push(num1 * num2);
      }

      // Handle division
      else if (str == "/")
      {
	 if (stack.GetLength() < 2)
	 {
	    cout << "Error: Not enough data for '" << str << "' operation\n";
	    return -1;
	 }
	 stack.Pop(num2);
	 stack.Pop(num1);
	 stack.Push(num1 / num2);
      }

      // Handle power
      else if (str == "^")
      {
	 if (stack.GetLength() < 2)
	 {
	    cout << "Error: Not enough data for '" << str << "' operation\n";
	    return -1;
	 }
	 stack.Pop(num2);
	 stack.Pop(num1);
	 stack.Push(pow(num1, num2));
      }

      // Handle absolute value
      else if (str == "abs")
      {
	 if (stack.GetLength() < 1)
	 {
	    cout << "Error: Not enough data for '" << str << "' operation\n";
	    return -1;
	 }
	 stack.Pop(num1);
	 stack.Push(fabs(num1));
      }

      // Handle square root
      else if (str == "sqrt")
      {
	 if (stack.GetLength() < 1)
	 {
	    cout << "Error: Not enough data for '" << str << "' operation\n";
	    return -1;
	 }
	 stack.Pop(num1);
	 stack.Push(sqrt(num1));
      }

      // Handle exp operation
      else if (str == "exp")
      {
	 if (stack.GetLength() < 1)
	 {
	    cout << "Error: Not enough data for '" << str << "' operation\n";
	    return -1;
	 }
	 stack.Pop(num1);
	 stack.Push(exp(num1));
      }

      // Handle log operation
      else if (str == "log")
      {
	 if (stack.GetLength() < 1)
	 {
	    cout << "Error: Not enough data for '" << str << "' operation\n";
	    return -1;
	 }
	 stack.Pop(num1);
	 stack.Push(log(num1));
      }

      // Handle unexpected operation
      else
      {
	 cout << "Error: Unexpected '" << str << "' in input\n";
	 return -1;
      }
      cin >> str;
   }

   // Error checking on stack
   if (stack.GetLength() < 1)
   {
      cout << "Error: Not enough data for '" << str << "' operation\n";
      return -1;
   }
   else if (stack.GetLength() > 1)
   {
      cout << "Error: Too much data for '" << str << "' operation\n";
      return -1;
   }

   // Print result
   stack.Pop(res);
   cout << "Result = " << res << endl;
   return 0;
}

//-----------------------------------------------------------
// Main program.
//-----------------------------------------------------------
int main()
{
   // Loop processing user input
   while (!cin.eof() && evaluate() != -1);
   return 0;
}