How to assign size to a globally declared 2d vector in the main function in C++?

Question

#include <bits/stdc++.h>
using namespace std;
vector< vector<int> >Adj;
int main()
{
    int n;
    cin>>n;
    Adj.assign(n);
}

This code doesn't work for assigning size to the vector.

Answer 1

1. Use resize method 'Adj.resize(n)'. The function alters the container's content in actual by inserting or deleting the elements from it.
2. If the given value of n is less than the size at present then extra elements are demolished.
3. If n is more than current size of container then upcoming elements are appended at the end of the vector