Finding sum of all elements of an array

#include<bits/stdc++.h>
using namespace std;

vector <int> v;

# define ll long long

ll indx(int n)
{
    if ( n==0 ) return v[0];
    ll ans=v[n]+v[indx(n-1)];
    return ans;
}

int main()
{
    cout<<"Enter number of elements : ";
    int n;
    cin>>n;

    v=vector <int> (n, 1);

    for ( int i=0 ; i<n ; i++) cin>>v[i];

    ll ans=indx(n-1);
    cout<<"Sum of all elements of the array : "<<ans;

    return 0;
}