positive array multi

#include <iostream>
#include <bits/stdc++.h>

using namespace std;

int main()
{
    int x,i=0;
    cin>>x;
double arr[x];

for(int i; i<x;i++){
    cout<<"arr["<<i<<"]:"<<endl;
   cin>>arr[i];

}

double sum;
for(int j;j<x;j++){

    if(arr[j]>= 0){
        sum*=arr[j];
    }
}

cout<<sum;
    return 0;
}