where is 2 dimensional array's size and how to use point to make 1 dimensional to 2?

just as the following code:

int a[100],b[10][10];

we declare two arrays,A 100 one dimensional and a 10*10 two dimensional.

My question is where is the size of b's line (10) store?

And,How could I use the type like c[][] to visit a element in a?

At present,I know two ways to do this,one is use define like

#define c[(x)][(y)] a[(x*10)+(y)]

the second is use memcpy to copy to a 2dimensional array.

Is there any other ways?

Thank you very much!