1. Initialize a two-dimensional vector, a vector of r*c, all values are 0.
vector<vector<int>> newOne(r, vector<int>(c, 0));
2. Use resize() to control the size
vector<vector<int>> res;
res.resize(r);//r line
for (int k = 0; k <r; ++k){ res[k].resize(c);//per line column c }