Google "cs50 gdb youtube" and you will find two helpful videos explaining how to use the debugger from the command line. It's much more reliable, and has the added benefit of being a tool that will always be available to you in the future even if you do not use the Cloud9 IDE for development.
Basically, to debug
myprog with a breakpoint at
myfunc, passing arguments
arg2, do the following:
gdb ./myprog break myfunc run arg1 arg2
After that, you can step forward with
n, or step into a function with
info args to view arguments,
info locals to view local variables, and
p foo to print the value of variable
To debug functions in multiple files, set your breakpoints and then as you are stepping through statements with
n, pay attention and when you get to the line that calls the externally-defined function, step into it with
The lastest version of the IDE has a new debug50 utility.