用时10分钟，一开始忘记保存小数点后两位了

#include<iostream>
#include<iomanip>
using namespace std;
double add(double n1,double n2)
{
    return n1+n2;
}
int main()
{
//  freopen("xxx.in","r",stdin);
//  freopen("yyy.out","w",stdout);
    double n1,n2;
    cin >> n1 >> n2;
    double j=add(n1,n2);
    cout << fixed << setprecision(2) << j;  
//  fclose(stdin); 
//  fclose(stdout);
    return 0;
}