Some useful hints to debug programs:

1. dbx can be used to step through the code and find the problem.
2. Generous use of printf statements to print the various information at the various steps can be helpful. It is better if the information printed is only one line long otherwise output is very cluttered.
3. All the debugging statements can be enclosed in #ifdef _DEBUG_ and #endif pairs. Then use #define _DEBUG_, at the beginning of the source file to enable debugging. For example,

#define _DEBUG_        /* Only once and at the begininng of any source file */ 
........
#ifdef _DEBUG_
	  printf("If I am here, there is a problem.  Count = %d\n", Count); 
#endif

The debugging statements can be disabled by removing the statement #define _DEBUG_.