2D vector passing by reference in C++

When i declare a vector like vector<vector<int> >v and try to pass it to a function like below it works :

int change(vector<vector<int> >&v)
{
    v[0][0]=-1;
}
int main()
{
    vector<vector<int> >v;
    int a[]={1,2,3};
    int b[]={4,5,6};
    v.push_back(vector<int>(a,a+3));
    v.push_back(vector<int>(b,b+3));
    change(v);
    cout<<v[0][0];
return 0;
}

But when i declare the vector like vector<int>v[2] and pass it to a function the same way? It's causing error :(

int change(vector<vector<int> >&v)
{
    v[0][0]=-1;
}
int main()
{
    vector<int>v[2];
    int a[]={1,2,3};
    int b[]={4,5,6};
    v[0]=vector<int>(a,a+3);
    v[1]=vector<int>(b,b+3);
    change(v);
    cout<<v[0][0];
return 0;
}

How can i do this and why this causing error?