Commonly used gdb commands
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gdb also understands abreviations of commands, so you can just type up to 
the unique part of a command name ("cont" for "continue", or "p" for "print")

help                  List classes of all gdb commands
help <topic>          Shows help available for topic or command

where     	      Shows stack: sequence of function calls executed so far
(or backtrace)        (good for pinpointing location of a program crash)
(or bt)

frame                 Shows all stack frames
frame <frame-num>     Sets current stack frame to <frame-num>

run                   Starts program at the beginning

break <line>          Sets breakpoint at line number <line>
break <func-name>     Sets breakpoint at beginning of function <func-name>
break main            Sets breakpoint at beginning of program
continue              Continues execution from breakpoint

condition <bp-num> <exp>   Sets breakpoint number <bp-num> to break only if
                           conditional expression <exp> is true

info break            Shows current breakpoints
disable [breakpoints] [bnums ...]  Disable one or more breakpoints
enable [breakpoints] [bnums ...]   Enable one or more breakpoints 
clear <line>          Clears breakpoint at line number <line>
clear <func-name>     Clears breakpoint at beginning of function <func-name>
delete <bp-num>       Deletes breakpoint number <bp-num>
delete                Deletes all breakpoints

step (or s)           Executes next line of program (steping into functions)
step <count>          Executes next <count> lines of program
next (or n)           Like step, but treats a function call as a single
next <count>            instruction
until <line>          Executes program until line number <line>

print <exp> (or inspect <exp>  Displays the value of expression <exp>
display <exp>         Automatic display of <exp> each time a breakpoint reached
whatis <exp>          Shows data type of expression <exp>
info locals           Shows local variables in current stack frame
set variable <variable> = <exp>   Sets variable <variable> to expression <exp>

list                  Lists next few lines of program
list <line>           Lists lines around line number <line> of program
list <start> <end>    Lists line numbers <start> through <end>
list <func-name>      Lists lines at beginning of function <func-name>

quit                  Quits gdb