polishcal.cpp

栈的应用—Polish Calculator

#include<iostream.h>
#include<cctype>
#include "PolishCal.h"


char get_command()
{
   char command;
   bool waiting = true;
   cout << "Select command and press <Enter>:";
   while (waiting) {
      cin >> command;
      command = tolower(command);
      if (command == '?' || command == '=' || command == '+' ||
          command == '-' || command == '*' || command == '/' ||
          command == 'q' ) waiting = false;
      else {
         cout << "Please enter a valid command:"   << endl
              << "[?]push to stack   [=]print top" << endl
              << "[+] [-] [*] [/]   are arithmetic operations" << endl
              << "[Q]uit." << endl;
      }
   }
   return command;
}


bool do_command(char command, MyStack &numbers)
/*
Pre:  The first parameter specifies a valid calculator command.
Post: The command specified by the first parameter
      has been applied to the Stack of numbers given by the second parameter.
      A result of true is returned unless command == 'q'.
Uses: The class Stack.
*/

{
   double p, q;
   switch (command) {
   case '?':
      cout << "Enter a real number: " << flush;
      cin >> p;
      if (numbers.push(p) == overflow)
         cout << "Warning: Stack full, lost number" << endl;
      break;

   case '=':
      if (numbers.top(p) == underflow)
         cout << "Stack empty" << endl;
      else
         cout << p << endl;
      break;

   case '+':
      if (numbers.top(p) == underflow)
         cout << "Stack empty" << endl;
      else {
         numbers.pop();
         if (numbers.top(q) == underflow) {
            cout << "Stack has just one entry" << endl;
            numbers.push(p);
         }

         else {
            numbers.pop();
            if (numbers.push(q + p) == overflow)
               cout << "Warning: Stack full, lost result" << endl;
         }
      }
      break;
  case '*':
      if (numbers.top(p) == underflow)
         cout << "Stack empty" << endl;
      else {
         numbers.pop();
         if (numbers.top(q) == underflow) {
            cout << "Stack has just one entry" << endl;
            numbers.push(p);
         }

         else {
            numbers.pop();
            if (numbers.push(q * p) == overflow)
               cout << "Warning: Stack full, lost result" << endl;
         }
      }
      break;    
  case '-':
      if (numbers.top(p) == underflow)
         cout << "Stack empty" << endl;
      else {
         numbers.pop();
         if (numbers.top(q) == underflow) {
            cout << "Stack has just one entry" << endl;
            numbers.push(p);
         }

         else {
            numbers.pop();
            if (numbers.push(q - p) == overflow)
               cout << "Warning: Stack full, lost result" << endl;
         }
      }
	  break;
	  
  case '/':
      if (numbers.top(p) == underflow)
         cout << "Stack empty" << endl;
      else {
         numbers.pop();
         if (numbers.top(q) == underflow) {
            cout << "Stack has just one entry" << endl;
            numbers.push(p);
         }

         else {
            numbers.pop();
            if (numbers.push(q / p) == overflow)
               cout << "Warning: Stack full, lost result" << endl;
         }
      }
	  break;
   case 'q':
      cout << "Calculation finished.\n";
      return false;
   }
   return true;
}