i want to create a 2D matrix using vector. why the below is wrong?

typedef std:vector<int> x

typedef std:vector<x> y

y matrix(7, x somevar(7) ) // trying to create 7 x 7 matrix

look the second index ... x some_var(7) , i have written explicitly to crete a vector of 7 elements using typedef and then repalcing that into the matrix as the second argument.

is it valid ?

if not why it is not valid and what i should i do ?

thanks