create matrix using vector c++ code example

Example 1: matrix in vector c++

vector<vector <int> > matrix;

cout << "Row's Length: " << matrix.size();
cout<< "Column's Length: "<< matrix[0].size();

Example 2: how to take input in 2d vector in c++

std::vector<vector<int>> d;
//std::vector<int> d;
cout<<"Enter the N number of ship and port:"<<endl;
cin>>in;
cout<<"\Enter preference etc..:\n";
for(i=0; i<in; i++){ 
cout<<"ship"<<i+1<<":"<<' ';
    for(j=0; j<in; j++){
    cin>>temp;
    d.push_back(temp);// I don't know how to push_back here!!
    }
}