I was just about to post asking for documents or tutorials on how to use gdb(GNU Debugger) to debug programs...but hey my friend google can help 

so here you go:
"the best ones that I liked"
http://www.yolinux.com/TUTORIALS/GDB-Commands.html
http://www.ibm.com/developerworks/library/l-gdb/
http://dirac.org/linux/gdb/
http://www.gnu.org/software/gdb/documentation/

and:
http://hubbard.engr.scu.edu/embedded/avr/doc/gnu/gdb/gdb.pdf
http://www.digilife.be/quickreferences/QRC/GDB%20Quick%20Reference.pdf
http://sourceware.org/gdb/current/onlinedocs/gdb.pdf.gz
http://www.stanford.edu/class/cs107/documents/gdbref.pdf
http://net.pku.edu.cn/~course/cs101/2007/resource/gdb-guidelines.pdf
http://erik.cabetas.com/stuff/debug/gdb-objC-tips.pdf
http://www.cs.princeton.edu/~benjasik/gdb/gdbtut.html
http://www.cs.cmu.edu/~gilpin/tutorial/
http://linux.bytesex.org/gdb.html
http://oucsace.cs.ohiou.edu/~bhumphre/gdb.html



of course you could just run gdb and type 'help' or type 'man gdb' to read gdb's manual.

Hope this helps