# start the debugger
gdb your-executable

# set a breakpoint
b some-method, break some-method

# run the program
r, run

# when a breakpoint was reached:

# run the current line, stepping over any invocations
n, next
# run the current line, stepping into any invocations
s, step
# print a stacktrace
bt, backtrace
# evaluate an expression and print the result
p length=strlen(string)
# list surrounding source code
l, list
# continue execution
c, continue

# exit gdb (after program terminated)
q, quit