表达式求值

#include <iostream>
#include <stack>
#include <cstring>
#include <unordered_map>
using namespace std;
typedef long long ll;
stack<int>num;
stack<char>op;
unordered_map<char,int>h{ {‘+‘,1},{‘-‘,1},{‘*‘,2},{‘/‘,2} };
void eval()
{
    int a=num.top();num.pop();
    int b=num.top();num.pop();
    char p=op.top();op.pop();
    int r=0;
    if(p==‘+‘)r=a+b;
    else if(p==‘-‘)r=b-a;
    else if(p==‘*‘)r=a*b;
    else if(p==‘/‘)r=b/a;
    num.push(r);
}
int main()
{
    string s;cin>>s;
    for(int i=0;i<s.size();i++)
    {
        if(isdigit(s[i])){
            int x=0,j=i;
            while(j<s.size()&&isdigit(s[j])){
                x=x*10+s[j]-‘0‘;j++;
            }
            num.push(x);
            i=j-1;
        }
        else if(s[i]==‘(‘){
            op.push(s[i]);
        }
        else if(s[i]==‘)‘){
            while(op.top()!=‘(‘)
                eval();
            op.pop();
        }
        else{
            while(op.size()&&h[op.top()]>=h[s[i]])
                eval();
            op.push(s[i]);
        }
    }
    while(op.size())eval();
    cout<<num.top()<<"\n";
}