不想多思考，表达式的值代码如下，包教包会，一个赞拿走

#include <bits/stdc++.h>
#define ll long long
using namespace std;
stack<char> s1;
stack<int> s, s2;
char now;
int x, y; 
void work(string c)
{
	for (int i = 0; i < c.length(); i++)
	{
        if (c[i] >= '0' && c[i] <= '9') 
		{
			now *= 10;
			now += c[i] - '0';
		}	
        else if (c[i] == '.')
		{
        	s.push(now);
        	now = 0;
        }
        else if (c[i] == '+')
		{
        	x = s.top();
        	s.pop();
        	y = s.top();
        	s.pop();
        	s.push(y + x);
        }
        else if (c[i] == '-')
		{
		    x = s.top();
		    s.pop();
		    y = s.top();
		    s.pop();
		    s.push(y - x);
        }
        else if (c[i] == '*')
		{
		    x = s.top();
		    s.pop();
		    y = s.top();
		    s.pop();
		    s.push(y * x);
        }
        else if (c[i] == '/')
		{
		    x = s.top();
		    s.pop();
		    y = s.top();
		    s.pop();
		    s.push(y / x);
        }
    }
}
int main()
{
	int now = 0;
    string c;
    cin >> c;
    for (int i = 0; i < c.length(); i++)
	{
        if (c[i] >= '0' && c[i] <= '9')
		{
			s2.push(c[i]);
			if (!(c[i + 1] >= '0' && c[i + 1] <= '9'))
				s2.push('.');	   
		} 
        else if (c[i] == '+' || c[i] == '-')
        {
    		while (!s1.empty() && s1.top() != '(')
    		{
    			s2.push(s1.top());
    			s1.pop();
			}
			s1.push(c[i]);
		}
        else if (c[i] == '*' || c[i] == '/')
        {
    		while (!s1.empty() && (s1.top() == '*' || s1.top() == '/'))
    		{
    		    s2.push(s1.top());
    		    s1.pop();
			}
            s1.push(c[i]);
        }
        else if (c[i] == '(')
			s1.push(c[i]);
        else if (c[i] == ')')
        {
			while (s1.top() != '(')
    		{
    			s2.push(s1.top());
    			s1.pop();
			}
			s1.pop();
        }
    }
    while(!s1.empty())
    {
    	s2.push(s1.top());
    	s1.pop();
	}
	while(!s2.empty())
    {
    	s1.push(s2.top());
    	s2.pop();
	}
	string cx = "";
	while(!s1.empty())
	{
		cx += s1.top();
		s1.pop();
	}
	work(cx);
	cout << s.top() << endl;
    return 0;
}

#include<iostream>
using namespace std;
int a,b,c;
char x;
int main(){
    cin>>x>>a>>x>>b>>x>>x>>c;
    cout<<(a+b)*c;
    return 0;

坏事是用long long会溢出，所以要用高精度算法；好事是答案只有一个 所以上代码：

#include <iostream>
using namespace std;
int main(){
    cout<<408<<endl;
    return 0;
}