Many are familiar with the hello world program in C

#include <stdio.h>

main ()
{
    printf ("hello world");
    return 0;

}

Why do some precede the main () function with int as in:

int main()

Also, I've seen the word 'void' entered inside the () as in:

int main(void)

It seems like extra typing for nothing, but maybe it's a best practice that pays dividends in other situations?

Also, why precede main() with an int if you're returning a character string? If anything, one would expect:

char main(void)

I'm also foggy about why we return 0 at the end of the function.