C++
#include <iostream>
using namespace std;

int main()
{
int n = 0;
cout << "Enter num: ";
cin >> n;
if (n >= 100 && n <= 999) {
int s = (n / 100) + ((n / 10) % 10) + (n % 10);
if (s % 3 == 0) {
cout << "Num multiple 3" << endl;
} else {
cout << "Num not multiple 3" << endl;
}
if (s % 5 == 0) {
cout << "Num multiple 5" << endl;
} else {
cout << "Num not multiple 5" << endl;
}
} else {
cout << "Error!" << endl;
}
return 0;
}