c++ vector 2d array push_back code example

Example 1: how to make a 2d vector in c++

// Create a vector containing n 
//vectors of size m, all u=initialized with 0
vector<vector<int> > vec( n , vector<int> (m, 0));

Example 2: 2d vector push back

std::vector<std::vector<int>> normal;
for(int i=0; i<10; i++)
{
  	//push a vector each time you loop a row
    normal.push_back(std::vector<int>());
    for(int j=0; j<20; j++)
    {
      	//push an item each time you loop a column
        normal[i].push_back(j);    
    }
}