Vector funct. adunare

#include <iostream>
using namespace std;

    int sum ( int a[100] )
    {
        int n;
        cout << "n = ";
        cin >> n;
        int i;

        for ( i = 1; i <= n; i++ ) {
            cout << "a[" << i <<"] = ";
            cin >> a[i];
      //   s = s + a[i];
        }
       int s = 0;
        for ( i = 1; i <= n; i++ ) {
            s = s + a[i];
        }

    cout << s << " ";
    }

int main(){

    //int n;
    //cout << "n = ";
    //cin >> n;


    int n;
   int a[100];
   cout << sum(a);


}