编辑代码

#include<iostream>     //输入的表达式要以'#'结尾，如‘5+6*3/(3-1)#’
#include<cstring>
#include<cstdio>
#include<cctype>
#include<stack>
using namespace std;
 
stack<char> opter;    //运算符栈
stack<double> opval;  //操作数栈
 
int getIndex(char theta)   //获取theta所对应的索引
{
	int index = 0;
	switch (theta)
	{
	case '+':
		index = 0;
		break;
	case '-':
		index = 1;
		break;
	case '*':
		index = 2;
		break;
	case '/':
		index = 3;
		break;
	case '(':
		index = 4;
		break;
	case ')':
		index = 5;
		break;
	case '#':
		index = 6;
	default:break;
	}
	return index;
}
 
char getPriority(char theta1, char theta2)   //获取theta1与theta2之间的优先级
{
	const char priority[][7] =     //算符间的优先级关系
	{
		{ '>','>','<','<','<','>','>' },
		{ '>','>','<','<','<','>','>' },
		{ '>','>','>','>','<','>','>' },
		{ '>','>','>','>','<','>','>' },
		{ '<','<','<','<','<','=','0' },
		{ '>','>','>','>','0','>','>' },
		{ '<','<','<','<','<','0','=' },
	};
 
	int index1 = getIndex(theta1);
	int index2 = getIndex(theta2);
	return priority[index1][index2];
}
 
double calculate(double b, char theta, double a)   //计算b theta a
{
	switch (theta)
	{
	case '+':
		return b + a;
	case '-':
		return b - a;
	case '*':
		return b * a;
	case '/':
		return b / a;
	default:
		break;
	}
}
 
double getAnswer()   //表达式求值
{
	opter.push('#');      //首先将'#'入栈opter
	int counter = 0;      //添加变量counter表示有多少个数字相继入栈，实现多位数的四则运算
	char c = getchar();
	while (c != '#' || opter.top() != '#')   //终止条件
	{
		if (isdigit(c))   //如果c在'0'~'9'之间
		{
			if (counter == 1)   //counter==1表示上一字符也是数字，所以要合并，比如12*12，要算12，而不是单独的1和2
			{
				double t = opval.top();
				opval.pop();
				opval.push(t * 10 + (c - '0'));
				counter = 1;
			}
			else
			{
				opval.push(c - '0');     //将c对应的数值入栈opval
				counter++;
			}
			c = getchar();
		}
		else
		{
			counter = 0;   //counter置零
			switch (getPriority(opter.top(), c))   //获取运算符栈opter栈顶元素与c之间的优先级，用'>'，'<'，'='表示
			{
			case '<':               //<则将c入栈opter
				opter.push(c);
				c = getchar();
				break;
			case '=':               //=将opter栈顶元素弹出，用于括号的处理
				opter.pop();
				c = getchar();
				break;
			case '>':               //>则计算
				char theta = opter.top();
				opter.pop();
				double a = opval.top();
				opval.pop();
				double b = opval.top();
				opval.pop();
				opval.push(calculate(b, theta, a));
			}
		}
	}
	return opval.top();   //返回opval栈顶元素的值
}
 
int main()
{
	//freopen("test.txt", "r", stdin);
	int t;     // 需要计算的表达式的个数
	cin >> t;
	getchar();
	while (t--)
	{
		while (!opter.empty())opter.pop();
		while (!opval.empty())opval.pop();
		double ans = getAnswer();
		cout << ans << endl<< endl;
		getchar();
	}
	return 0;
}