calc.cpp

《c++ 实践之路》光盘中的源代码

// (c) Bartosz Milewski 2000
#include "Calc.h"
#include "Input.h"
#include <iostream>
#include <cassert>

bool Calculator::Execute (Input const & input)
{
	int token = input.Token ();
	bool status = false; // assume failure

	if (token == tokError)
	{
		std::cout << "Unknown token\n";
	}
	else if (token == tokNumber)
	{
		if (_stack.IsFull ())
		{
			std::cout << "Stack is full\n";
		}
		else
		{
			_stack.Push (input.Number ());
			status = true; // success
		}
	}
	else
	{
		assert (token == '+' || token == '-' 
			 || token == '*' || token == '/');
		if (_stack.IsEmpty ())
		{
			std::cout << "Stack is empty\n";
		}
		else
		{ 
			int num2 = _stack.Pop ();
			int num1;

			// Special case, when only one number on the stack:
			// use this number for both operands.

			if (_stack.IsEmpty ())
				num1 = num2;
			else
					num1 = _stack.Pop ();

			_stack.Push (Calculate (num1, num2, token));
			status = true;
		}
	}
	return status;
}

int Calculator::Calculate (int num1, int num2, int token) const 
{ 
	int result;

	if (token == '+') 
		result = num1 + num2; 
	else if (token == '-') 
		result = num1 - num2; 
	else if (token == '*') 
		result = num1 * num2; 
	else if (token == '/') 
	{ 
		if (num2 == 0) 
		{ 
			std::cout << "Division by zero\n"; 
			result = 0; 
		} 
		else 
			result = num1 / num2; 
	} 
	return result; 
} 

int main ()
{
	Calculator TheCalculator;
	bool status;
	do
	{
		// Prompt for input
		std::cout << "> ";
		Input input;
		status = TheCalculator.Execute (input);
		if (status)
		{
			for (StackSeq seq (TheCalculator.GetStack ());
				 !seq.AtEnd ();
				 seq.Advance () )
			{
				std::cout << "    " << seq.GetNum () << std::endl;
			}
		}
	} while (status);
}