initialising 2d vector

1auto M = 4;	// num of rows
2auto N = 3; // num of cols in each row
3auto default_value = 1; // default value of all int elements
4std::vector<std::vector<int>> matrix(M, std::vector<int>(N, default_value));

1  // Create a vector containing n row and m columns
2  vector<vector<int> > vec( n , vector<int> (m, 0));  

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