to it's look like this

vector<string>ans;
// Recursive function to print all
// possible subsequences for given array
void printSubsequences(string arr[], int index,
                       vector<string> subarr,int n)
{
    // Print the subsequence when reach
    // the leaf of recursion tree
    if (index == n)
    {
        string s = "";
        for (auto it:subarr){
            s += it;
        }
        ans.push_back(s);
        return;

    }
    else
    {
       //pick the current index into the subsequence.
        subarr.push_back(arr[index]);
       
 
         printSubsequences(arr, index + 1, subarr,n);
 
         
        subarr.pop_back();
       
      //not picking the element into the subsequence.
        printSubsequences(arr, index + 1, subarr,n);
    }
    
}
int main()
{

    string arr[]={"01", "111", "1001", "0011"};
    int n=4;
    vector<string> vec;
    printSubsequences(arr, 0, vec,n);

    // check here
    for(auto i : ans){
        cout<<i<<" ";
    }cout<<endl;

    return 0;
}

Thank you a lot