gcc error: expected expression before 'else'

gcc error: expected expression before 'else'

I'm wondering why such code generates following error while compiling:
1.c:11: error: expected expression before 'else'
code:
#include <stdio.h>
#define xprintk(...) while(0);
int main (void)
{
if (1)
xprintk("aaa\n");
else
xprintk("bbb\n");
return 0;
}