What are the different valid prototypes of 'main' function? [duplicate]

Answer 1

The C standard (§ 5.1.2.2.1) defines two entry point prototypes:

int main(void);

or

int main(int argc, char **argv);

Other than that, every OS has its own additional non-standard entry points. WinMain, etc.

Answer 2

The full prototype allowed by gcc is:

int main(int argc, char * argv[], char *envp[])

but envp is rarely used. Omitting argc and argv is also considered acceptable.