void main(void)
is allowed by some(all?) C compilers. However, it should not be used anyway. Because at least since C99 is it not allowed. However, I did not find a C compiler which complains about it.
E.g. void.c:
#include <stdio.h>
void main(void)
{
printf("hello world");
}
gcc void.c
Compiles. Also check http://www.compileonline.com/compile_c_online.php
So in conclusion (even though I do not find references): In earliest C versions void main(void)
was probably not forbidden.
However: Without specifying a return value, you just do not now what your program returns. So, standard or not, correct or false, do not use it, because it makes your program non-deterministic.