GDB (The GNU Debugger)
Command: gdb>               Discription
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b   linenumber              Set breatpoint
r                           Run program
c                           Continue execution
b   filename:#num           Set breakpoint in different file
s                           Step program
n                           Step over functions
p   varname                 Print value of variable
disp    varname             Print value of var and turns p on
del $num                    Turn off breakpoint or display
h                           Help on commands
q                           Quit GDB