算术表达式的运算

大二写的作业，大三还有用，在这里记录一下。

#include
#include
#include
#include 
using namespace std;
class Stack
{
public:
	Stack();
	~Stack() { MakeEmpty(); }
	double numin(const char ch, double s);
	void charin(const char ch);
	void pushnum(double);
	void pushchar(int, const char);
	double popnum();
	char popchar();
	double calculate();
	void MakeEmpty();
	double GetAns() { return numtop->data; }
	char GetCharTopch() { return chartop->ch; }
private:
	class NumNode //用来存数
	{
	public:
		double data;
		NumNode *next;
		NumNode(double d, NumNode *p) :data(d), next(p) {}
		NumNode() {}
	};
	class CharNode //用来存符号
	{
	public:
		int data;
		char ch;
		CharNode *next;
		CharNode(int d, char c, CharNode* p) :data(d), ch(c), next(p) {}
		CharNode() {}
	};
	NumNode* numtop;
	CharNode* chartop;
};

Stack::Stack()
{
	chartop = new CharNode;
	numtop = new NumNode;
	if (!chartop) { cerr << "内存分配错误！" << endl; exit(1); }
	chartop->ch = '@';
	chartop->data = -1;
	chartop->next = 0;
	numtop = 0;
}
double Stack::numin(const char ch, double s)
{
	s = (ch - 48) + s * 10; //原来的结果乘10加上新的数字
	return s;
}
void Stack::charin(const char ch)
{
	if (!(ch >= '0'&&ch <= '9'))
	{
		int outvalue = -1;
		//对除了)的符号赋运算优先值
		if (ch == '+' || ch == '-')
			outvalue = 2;
		else if (ch == '*' || ch == '/' || ch == '%')
			outvalue = 4;
		else if (ch == '(')
			outvalue = 6;
		
		//运算时，先前符号优先于当前符号的情况
		CharNode* t = chartop;
		while (outvalue <= t->data&&t->ch != '@')
		{
			//如果遇到的是')'，之前有'('就把两个符号
			if (t->ch == '('&&ch == ')')
			{
				popchar();
				break;
			}
			t = t->next;
			pushnum(this->calculate());
		}
		if (ch != '('&&ch != ')')
			this->pushchar(outvalue, ch);
		else if (ch == '(')
			this->pushchar(0, ch);
	}
}
void Stack::pushnum(double x)
{
	numtop = new NumNode(x, numtop);
}
void Stack::pushchar(int x, const char ch)
{
	chartop = new CharNode(x + 1, ch, chartop);
}
double Stack::popnum()
{
	if (numtop == NULL) return 0;
	NumNode *temp = numtop;
	numtop = numtop->next;
	double x = temp->data;
	delete temp;
	return x;
}
char Stack::popchar()
{
	if (chartop == NULL) return ' ';
	CharNode *temp = chartop;
	chartop = chartop->next;
	char ch = temp->ch;
	delete temp;
	return ch;
}
double Stack::calculate()
{
	double res = 0.0;
	CharNode* t = chartop;
	t = t->next;
	char ch = popchar();
	while (ch == '(')
	{
		t = t->next;
		ch = popchar();
	}
	if (ch == '@')
		return popnum();
	double a = popnum();
	double b = popnum();
	switch (ch)
	{
	case '+':
		res = a + b;
		break;
	case '-':
		res = b - a;
		break;
	case '*':
		res = a * b;
		break;
	case '/':
		res = b / a;
		break;
	case '%':
		res = b - int(b / a)*a;
		break;
	default:
		break;
	}
	return res;
}
void Stack::MakeEmpty()
{
	NumNode* t1 = numtop;
	CharNode* t2 = chartop;
	while (numtop)
	{
		t1 = numtop;
		numtop = numtop->next;
		delete t1;
	}
	while (chartop)
	{
		t2 = chartop;
		chartop = chartop->next;
		delete t2;
	}
}
int main()
{
	int i = 0, mark = 0, mode = 1;
	Stack OpStack;
	double ans = 0.0, s = 0.0, s1 = 0.0;
	char ch[20];
	cout << "请输入一个表达式:";
	cin >> ch;
	while (ch[i] != '')
	{
		if (ch[i] == '.') 
		{
			mode = 2;
			mark = 0; //初始化mark
		}
		else if (isdigit(ch[i]))
		{
			s1 = OpStack.numin(ch[i], s1); //原来的结果乘10加上新的数字
			if(mode==2)
				++mark; //记录有多少位小数
			if (!(isdigit(ch[i + 1])) && ch[i + 1] != '.')
			{
				s = s1/ pow(10.0, mark);//得到最终入栈的数
				//计算完成，复位
				OpStack.pushnum(s); mode = 1; s = 0.0;
				s1 = 0;  mark = 0;
			}
		}
		else
			OpStack.charin(ch[i]);
		++i;
	}
	while (OpStack.GetCharTopch() != '@')
	{
		OpStack.pushnum(OpStack.calculate());
	}
	cout << OpStack.GetAns() << endl;
	return 0;
}