how to declare 2d vector in c++ code example

Example 1: 2d vector c++ declaration

vector< vector> a(rows, vector (cols));

Example 2: initialising 2d vector

// Initializing 2D vector "vect" with 
// values 
vector > vect{ { 1, 2, 3 }, 
                           { 4, 5, 6 }, 
                           { 7, 8, 9 } };

Example 3: how to take input in 2d vector in c++

std::vector> d;
//std::vector d;
cout<<"Enter the N number of ship and port:"<>in;
cout<<"\Enter preference etc..:\n";
for(i=0; i>temp;
    d[i].push_back(temp); 
    }
}