Q:

Can I omit return from main in C?

In C++, 3.6.1 Main function

(3.6.1/5) A return statement in main has the effect of leaving the main function (destroying any objects with automatic storage duration) and
  calling exit with the return value as the argument. If control reaches
  the end of main without encountering a return statement, the effect is
  that of executing return 0;

Can I do the following in C99 without return 0?
int main() { }

A:

Yes, as of C99, reaching the } at the end of main returns 0 if the return type of main is compatible with int.

5.1.2.2.3 Program termination
If the return type of the main function is a type compatible with int, a return from the initial call to the main function is equivalent to calling the exit function with the value returned by the main function as its argument;11) reaching the } that terminates the main function returns a value of 0. If the return type is not compatible with int, the termination status returned to the host environment is unspecified.

A:

Yes, the C99 standard says (§5.1.2.2.3):

reaching the } that terminates the main function returns a value of 0.

