It's an abuse of the standard (c90 and c99). main is supposed to return int and take either no arg or two args, but I think a lot of legacy code violates this,

It's an abuse of the standard (c90 and c99). main is supposed to return int and take either no arg or two args, but I think a lot of legacy code violates this, so most compilers let you off with a warning. That said, "-Wall -Werror" are two useful things to always add to your gcc invokation.