push back in 2 D vectors code example

Example: 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);    
    }
}