When you use scanf(), generall you can check the return value of scanf(). If the return value is equal to -1, it means that it gets the end of input. Besides, you when you use cin, you can just judge if the input is end by the return value of cin is 0 or not. If it is 0, it means the end.
eg:
int main(){
    int n;
    while(scanf("%d", &n) != -1){
    ....
    }
}

and

int main(){
    int n;
    while(cin >> n){
    ....
    }
}