//支持带括号的表达式,支持+-*/、^(指数)、取负、!(阶乘)
#include <iostream>
#include <stack>
#include <math.h>

using namespace std;

double inStack();   //核心函数，将操作符有序的入栈计算， 最后返回结果
void calculate(stack<char>& Ope, stack<double>& Num);  //用来计算加减乘除, 结果放在数字栈顶
void factorial(stack<double>& Num);   //用来计算阶乘
int priority(char ope_);   //用来计算操作符的优先级

int main() {
double result;   //最后的结果


cout << "请输入：\n";
result = inStack();   //将缓冲区的操作符和数字压入栈

cout << "结果是：\n" << result;

return 0;

}
double inStack() {
stack<char> Ope;
stack<double> Num;
char ope_;
double num_;

while (1) {
if (cin.peek() >= '0' && cin.peek() <= '9') {  //判断下一个是否是数字
cin >> num_;
Num.push(num_);   //数字直接入栈
}
else {
cin >> ope_;
if (ope_ == '=') {
while (!Ope.empty()) calculate(Ope, Num); //如果符号栈不空，就一直计算
return Num.top();  //如果是等号且符号栈顶为空，就返回数字栈顶元素

}
else if (ope_ == '!') factorial(Num);  //如果是！就阶乘
else if (ope_ == '(' || Ope.empty()) Ope.push(ope_);    //如果符号是左括号或符号栈为空直接压入
else if (ope_ == ')') {  //如果是右括号
while (Ope.top() != '(') calculate(Ope, Num); //一直计算完括号里的
Ope.pop();  //左括号出栈
}
else if (priority(Ope.top()) >= priority(ope_)) {  //如果栈顶符号的优先级大于等于当前
while (Ope.top() != '(') {
calculate(Ope, Num);   //计算结果压入数字栈,取出当前栈顶
if (Ope.empty() || priority(Ope.top()) < priority(ope_)) break;  //当符号栈为空或者待压入的符号优先级高就跳出
}
Ope.push(ope_);  //压入当前符号
}
else Ope.push(ope_);  //否则就压入符号栈
}
}
}

void calculate(stack<char>& Ope, stack<double>& Num) {
double a, b;

if (Ope.top() == '-') {
a = Num.top(); Num.pop();
Ope.pop();   //取出负号
if (!Num.empty()) {
if (Ope.empty()|| Num.size() == Ope.size())
Ope.push('+');  //如果前面还有数字，就压入+，即变成加负值
}
Num.push(-a);  //压入负值
}
else {
a = Num.top(); Num.pop();
b = Num.top(); Num.pop();

if (Ope.top() == '+') Num.push(b + a);
else if (Ope.top() == '*') Num.push(b * a);
else if (Ope.top() == '/') Num.push(b / a);
else if (Ope.top() == '^') Num.push(pow(b, a));

Ope.pop();
}
}

void factorial(stack<double>& Num) {
int a = static_cast<int>(Num.top());Num.pop();
int result = 1;

for (int i = 1; i <= a; i++) result *= i;

Num.push(static_cast<double>(result));
}

int priority(char ope_) {
if (ope_ == '(') return 0;
else if (ope_ == '+' || ope_ == '-') return 1;
else if (ope_ == '*' || ope_ == '/') return 2;
else if (ope_ == '^') return 3;
}