简单！

#include <bits/stdc++.h>
using namespace std;
int main () {
    string a;
    double b;
    cin >> a >> b;
    if(a == "ceil") cout << ceil(b);
    if(a == "floor") cout << floor(b);
    if(a == "round") cout << round(b);
    return 0;
}

OK啦，一个一个判断就可以啦