Own assert() -> Segmentation fault

[StreamKid]

why is a segmentation fault caused in this simple thing???
and what exactly is this kind of error???
sorry, n00b things :/

******************************************************
*#define DEBUG
*#include <cstdio>
*
*#define assert( x ) \
*       if( ! ( x )) \
*       { \
*               printf( "\nERROR!! Assert %s failed", #x ); \
*               printf( "\n on line %s", __LINE__ ); \
*       }
*
*
*int main()
*{
*       int x = 5;
*       printf( "first assert" );
*       assert( x == 6 );
*       return 0;
*}
******************************************************
******************************************************
*first assert
*ERROR!! Assert x == 6 failed
*Segmentation fault
******************************************************