expressioncalculator.cpp

用VC写的一个根据输入的数学表达式字符串求出结果

// ExpressionCalculator.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <string>
#include <stack>
using namespace std;
int Compute(int l,int r,const char& c)
{
	if(c == '-')
		return r - l;
	if(c == '+')
		return l + r;
	if(c == '*')
		return l * r;
	if(c == '/')
	{
		if(r == 0)
			throw string("Denominator cannot be zero value");
		else
		return l / r;
	}
}

void StackOperator(stack<int>& Operand,stack<char>& Operator)
{
	int r,lside,rside;
	rside = Operand.top();
	Operand.pop();
	lside = Operand.top();
	Operand.pop();
	r = Compute(lside,rside,Operator.top());
	Operator.pop();		
	Operand.push(r);
}

int Calculator(const string& Expression)
{
	int num = 0,result = 0;
	char c;
	stack<char> Operator,SOperator;
	stack<int> Operand,SOperand;
	for(int i = 0; i < Expression.length(); i++)
	{
		c = Expression[i];
		if( c >= '0' && c <= '9')
		{
			num = num * 10 + c - '0';
			if(i != Expression.length() - 1)
			{
				if(Expression[i+1] > '9' || Expression[i+1] < '0')
					Operand.push(num);
			}
			else
			{
				Operand.push(num);
			}
		}
		else if( c == ')')
		{
			StackOperator(Operand,Operator);
		}
		else if(c == '+'|| c == '-'|| c == '*'|| c == '/')
		{
			num = 0;
			Operator.push(c);
		}
	}
	while(!Operator.empty())
	{
		if(Operator.top() == '+' || Operator.top() == '-')
		{
			SOperator.push(Operator.top());
			SOperand.push(Operand.top());
			Operator.pop();
			Operand.pop();
		}
		else
		{
			StackOperator(Operand,Operator);
		}
	}
	SOperand.push(Operand.top());
	Operand.pop();

	while(!SOperator.empty())
	{
		StackOperator(SOperand,SOperator);
	}
	return SOperand.top();
}

int _tmain(int argc, _TCHAR* argv[])
{
	string Expression;
	int result;
	getline(cin , Expression , '\n');
	try{
		cout<<Calculator(Expression)<<endl;
	}
	catch(const string& msg)
	{
		cout<<msg<<endl;
	}

	return 0;
}