geany is definetly missing a debugger(interface).
Though there exists a plugin called geanydbg as an integrated frontend for gdb, it is not in the repositories and compiling it oneself gives quite some problems (gtk+-2 bla bla), here is how to get it working (without compiling anything):

1. make sure gdb (the actual debugger) is installed
2. upgrade geany to 0.17(-1) through the debian unstable repository
3. download geanydbg plugin from here:
========= SCRAPER REMOVED AN EMBEDDED LINK HERE ===========
url was:"http://ftp.cica.es/ubuntu/ubuntu/pool/universe/g/geanygdb/geany-plugin-gdb_0.0.2-0ubuntu1_i386.deb"
linktext was:"http://ftp.cica.es/ubuntu/ubuntu/pool/u ... 1_i386.deb"
====================================
(of course depending on your architecture)
4. goto to folder it has been downloaded and install it by: $ sudo dpkg -i geany-plugin-gdb_0.0.2-0ubuntu1_i386.deb

Now a debugger panel is available next to the"Documents" and"Symbols" Tabs