不知道有什么错

#include <iostream>
using namespace std;
int main(){
int num, res;
int n1 ,n2 ,n3;

cin >> num;
n3 = (num - num%100)/100;
n2 = num%100-(num%100)%10;
n1 = (num - 100*n3-n2)*100;
cout << n1+n2+n3;
return 0;

}