Use gdb for debugging your program

For a not so friendly os like unix, gdb is quite user friendly debugger. You can use gdb to locate bugs in your program, trace variables, find out how your recursive functions work etc.

First step would be compilation of your program with -g flag. -g flag will enable gdb to used with the program
gcc -g myfile.c -o myfile
Next you run gdb on the executable program, in this case myfile.
gdb myfile

Some of the important commands to be used within gdb are

command	Usage	Description
run	run run par r	execute the program till end or till first break point
break	break 3 break myfunction	Set a break point at the given line or function
step	step step 2	Execute one statement or n statements if arg is given
list	list list n list function list file:function	List the source program List around the given line num List the function (of the given file)
print	print a print num+3 print/x num	Print value of expression or var with format if specified (last one prints num in hex)
display	display num display a+b	Print the value of expression each time program stops
backtrace	backtrace bt	Prints backtrace of all the stack frames (and thus function calls)
frame	frame 1 frame 0	Display content of nth frame
quit	quit q	Quit gdb
help	help help list help running help stack	Print help of a command or a category
continue	continue	Continue till next break point or end
finish	finish	Execute till the current function ends
clear	clear clear 8	Clear the break point at current line or line specified

Now look at this screen shots to understand the usage