2D array question

[v8902477 at cc.nu.oz.au]

	Hello,  could somebody please help me with the following? I'm attempting
to create a two dimensional array at run time using calloc.  The array is an
array of structures like this :

	struct a {
		int a1, a2, a3;
	};

And I'm using :

	array = (struct a *) calloc(xdim*ydim, sizeof(struct a));

to allocate space for the array.  xdim and ydim are the dimensions.  I believe
this correct.  It seems to work.  The problem came when I attempted to assign a
value to an element in the array.  I tried it this way :

	*((array+x+y*ydim).a1) = value;

Am I correct with this?  If array is a pointer it's okay to add integers to it
and use the sum as a pointer, is it not?  I get an error stating that .a1 is not
a valid lvalue.  Should I be using -> somewhere?

Help please!

Bernard.

Sorry if this has been asked before.