Why isn't C array initialization syntax allowed for arbitrary assignments?

Question

I was trying to learn the array fundamentals in Java and this question arises:

Version 1:

int[] x  = {12,34,56,78};

Version 2:

int[] x;  
x = {12,34,56,78};

Version 1 is correct but version 2 is incorrect.

Why is this the case? What is the story behind it?
Please, describe this from a compiler-oriented point of view.

Answer 1

The compiler needs to know how much storage to allocate for the array when it is declared.

int x[] = {12,34,56,78};

In this case the compiler knows that it needs storage for four integers; this is comparable to saying int x[4].

int x[];
/* ... */
x = {12,34,56,78};

However, in this case the compiler sees int x[] and knows it must allocate space for an array but it doesn't know how much until it gets to the following line, at which time it is too late.