he recommended approach is to use fill constructor to initialize a two-dimensional vector with a given default value : std::vector<std::vector<int>> fog(M, std::vector<int>(N, default_value)); where, M and N are dimensions for your 2D vector. code example
Example: initialize 2d vector of ints c++
auto M = 4; // num of rows
auto N = 3; // num of cols in each row
auto default_value = 1; // default value of all int elements
std::vector<std::vector<int>> matrix(M, std::vector<int>(N, default_value));