小算法--括号匹配

#include<iostream>
#include<string>
#include<vector>
using namespace std;

int main(int argc,char* argv[])
{
    string str;
    vector<char> elem;
    cin>>str;
    char temp = ' ';
    int i = 0;
    bool flag = true;
    while(str[i] != '\0'){
        if(str[i] == '{' || str[i] == '[' || str[i] == '('){
            elem.push_back(str[i]);
        }else if(str[i] == '}' || str[i] == ']' || str[i] == ')'){
            temp = elem.back();
            elem.pop_back();
            if((temp == '{' && str[i] == '}')||(temp == '[' && str[i] == ']')||(temp == '(' && str[i] == ')')){

            }else{
                flag = false;
                break;
            }
        }
        i++;
    }
    if(flag){
        cout<<str<<"is good"<<endl;
    }else{
        cout<<str<<"is bad"<<endl;
    }
    return 0;
}