Vectors- Basic Doubt

[ofey]

I am very new to vectors and would like know how assignment works in case of a vector of vectors [2-D Vector].
I want to input a list of elements(from stdin) to the first row of the vector of vectors. How should I go about it?
I tried to assign it as-

 for(loopVar1=0;loopVar1<sizeOfSequence;loopVar1++) {
            cin>>element;
            vector1[0][loopVar1]=element;
     }

I realize that this is naive and is throwing a seg fault. I know how .push_back works in case of 1-D vectors but am not sure what to do here. Please help.

[MiiNiPaa]

 for(loopVar1=0;loopVar1<sizeOfSequence;loopVar1++) {
            cin>>element;
            vector1[0].push_back(element);
     }

[vlad from moscow]

std::vector<std::vector<int>> v;

v.push_back( std::vector<int>() );

const int N = 10;

v[0].reserve( N );
 
for ( int i = 0; i < N; i++ )
{
   std::cout << "Enter a number: ";
   int x;
   std::cin >> x;
   v[0].push_back( x );
}

[ofey]

Thank you.