set 2D vector to 0 in C++ code example

Example 1: initializing 2d vector

vector<vector<int> > vec( n , vector<int> (m, 0));

Example 2: initialise 2d vector in c++

// Initializing 2D vector "vect" with 
// values 
vector<vector<int> > vect{ { 1, 2, 3 }, 
                           { 4, 5, 6 }, 
                           { 7, 8, 9 } };