Two dimensional arrays "C question"

Hello,

My question has to do with two dimensional arrays. Please consider the
following code:

==================================
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

char greet [] [8]=
{"Hello",
"Holla",
"Bonjour",
"Ciao"};

int main ()
{
int u;
u = strlen(greet[2]);
return 0;
}
===============================

In the above snippet, the compiler automatically calculates the number of
items for the first dimension subscript. So in reality it knows that there is
4 string of atleast 8 characters long... like this:
  
char greet [4] [8]=
{"Hello",
"Holla",
"Bonjour",
"Ciao"};
....

So we see that the compiler can automatically calculate the first dimension.
But consider the following code snippet and I don't understand why the
compiler is not able to calculate the first dimension like it did in the
above sample code:

===============================
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

typedef struct abc
{
int zzz[2];
char a[][8];
}ABC;

typedef struct menu
{
struct abc *pColl;
}MENU;

MENU *F1(MENU *pC, ABC a[])
{
pC = malloc (sizeof (struct menu));
pC->pColl = a;
return pC;
}

int main ()
{
int u;
MENU *pMenu = NULL;
ABC x[] =
{
10, 20,
{"sss",
"ttthhh"}
};

pMenu = F1(pMenu, x);
u = strlen(pMenu->pColl[0].a[1]);

free(pMenu);
return 0;
}
==================================

I must be getting confused with the extra lines of code here. However I get
the following errors:

c:\dts_visual_c++\test1\test1\twodimenarray2.c(17) : error C2233: 'a' :
arrays of objects containing zero-size arrays are illegal

c:\dts_visual_c++\test1\test1\twodimenarray2.c(28) : error C2233: 'x' :
arrays of objects containing zero-size arrays are illegal

If I do this:

char a[2][8];

It compiles without errors though!

Why isn't the compiler able to calculate the first dimension for the latter
sample of code?

All help appreciated!

--
Best regards
Roberto