SOS!!! About Coredump

I am developing app using Mandrake 6.1(gcc 2.91). To Debug App, When I set ulimit=0 , App exit with print "Segmentation fault", of course , no core file produce. But When I set ulimit = 10000(any value), App DON'T exit without output, core file procuded, But is null, and more, this process may become zombin process, nouse with "kill -9" command, * App is my test program, very simple. HELP!!! Gone With Wind