GCC does not support // annotation Solution

This time is written using slickeditCode(Cygwin is installed on Windows.) the GCC is used by the compiler, but the following error occurs during compilation when "//" is used to write comments: Error: parse error before '/'token, extra tokens at end of # endif direve ve. Today, I found some clues on the Internet. In the slickedit build menu, GNU C option -- "complie --"Support ANSI standard, no GNU extensions (-ANSI ),It turns out that I 've hooked this up, and now it's okay not to tick it. 
That is to say, GCC-ANSI will cause the problem of not recognizing "//". The specific reason is unknown.