How to use #ifdef to C/C++

example

int testfunc(int x, int y)

{

#ifdef  _DEBUG

      printf("x=%d, Y=%d", x,y);  // if x=1, y =2 

#endif

   return  (x * Y) ;

}

if debug mode
#define _DEBUG "DEBUG"

print x=1, Y=2

after return

if release mode,

not print

return