What does `:>` (colon, greater than, aka. smile face) mean in C Programming Language? [duplicate]

Question

recently I ran into a strange grammar of C Programming Language.

First, let's see the code:

main(void) {
int a[10:> ;
printf("asdf");
return 0;
}

And you can compile it with gcc:

/tmp  gcc sample.c
sample.c: In function ‘main’:
sample.c:3: warning: incompatible implicit declaration of built-in function ‘printf’

As you can see, there's no error or any warning related to it. So this means :> equals to ] in CPL?

How can that happen?

BTW: I'm using gcc 4.2.1.