好像可以直接+0.5取整,真没想到就

#include <iostream>

using namespace std;

int main()
{
    double x;
    while(cin>>x)
    {
        if((long long)(x*10)%10>=5)
        {
            cout<<(long long)x+1<<endl;
        }
        else
        {
            cout<<(long long)x<<endl;
        }
    }
    return 0;
}