conditional compile...

hello all,

i wrote the small program below to practice conditional compiling. if i define MYSYMBOL then everthing works fine, but when i comment MYSYMBOL gcc gives the following message:
cnd_compile01.c:4:2: error: #error "Error"
cnd_compile01.c:1: warning: ISO C forbids an empty source file

i cant understand the warning and how to eliminate it? i tried placing some dummy comment but still the same warning.

also why is compiler printing error twice. it looks ugly. is there a way to make it print error once only?

thanks.

code:
/* #define MYSYMBOL 1 */

#if MYSYMBOL != 1
#error "Error"
#else

#include <stdio.h>
main() { puts("hello"); }

#endif
.

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