#include<iostream>
#include"stack.h"

using namespace std;

int main()
{
  Stack s;
  char c;
  float v1, v2, v3;
  bool done=false;

  // The loop below reads the input, one operator at a time,
  // and carries out the operation depending on the operator.
  // It stops upon receiving 'q' or if the read fails.
  while (!done) {

    if (!(cin >> c)) {
      cout << "Error: cannot read input\n";
      break;
    }

    switch (c) {
    case '?':
      if (!(cin >> v1)) { // Read the float input
        cout << "Error: cannot read float\n"; // cin failed to read the float
        done = true;                          // so we stop
      }
      else if (!s.Push(v1))
	  cout<<"Stack Overlow!\n";
      break;

    case '+':     // Handle all the arithmetic operators similarly
    case '-':
    case '*':
    case '/':
      if(!s.Pop(v1)) {
        cout<<"Stack Empty!\n";
	break;
      }
      if(!s.Pop(v2)) {
	s.Push(v1);
        cout<<"Stack Has Only One Entry!\n";
	break;
      }

      // We already know c is an arithmetic operator;
      // v1 and v2 are the operands
      // now perform the operation and put the result in v3
      switch (c) {
      case '+':
        v3=v2+v1;
        break;
      case '-':
        v3=v2-v1;
        break;
      case '/':
        v3=v2/v1;
        break;
      case '*':
        v3=v2*v1;
        break;
      }
      if (!s.Push(v3))
	  cout<<"Stack Overlow!\n";
      break;

    case '=':     // Print the top of the stack by pop-print-push
      if(!s.Pop(v1)) {
        cout<<"Stack Empty!\n";
	break;
      }
      cout << v1 << "\n";
      if(!s.Push(v1))
	  cout<<"Stack Overlow!\n";
     break;

    case 'p':     // Pop the top
      if(!s.Pop(v1))
        cout<<"Stack Empty!\n";
      break;

    case 'q':     // Quit
      done=true;
      break;

    default:
      cout<<"Invalid Entry!\n";
      break;
    }
  }

  return 0;
}