为什么50（5,6,7,8,9）求助

#include <iostream>
#include <algorithm>
using namespace std;
struct student {
    int tt,yf,zf;
};
bool comp (student a,student b)
{
    return a.zf>b.zf;
    return a.yf>b.yf;
    return a.tt<b.tt;
}
int main()
{
    int n,i,sf,yyf;
    cin>>n;
    student a[n];
    for (i=0;i<n;i++)
    {
        cin>>a[i].yf>>sf>>yyf;
        a[i].zf=a[i].yf+sf+yyf;
        a[i].tt=i+1;
    }
    sort (a,a+n,comp);
    for (i=0;i<5;i++) cout<<a[i].tt<<' '<<a[i].zf<<endl;
    return 0;
}