Thumb of Rules

Function Interface Design
* Write function comment in the head of each function
* Give a good name to each function and avoid using undefined verbs
* Return a status and pass the desired return values by pointers
* The number of input paramters is no more than 7. Othrewise use struct
* Write function prototype and keep data types of input and return parameters match their declarations and no casting
* Const qualified read-only parameter to which input pointers point
* Follow some order of input parameters, like (dst, src, num)
* Check the legitimacy of input parameters and input global variables by using `assert'
* Avoid using input parameters, esp. pointers, as working variables. Use their local copies
* Check the legitimacy of function return value, esp. the return value of std library functions
* Use macros to replace variables of multiple references (i.e., of very long names)

Function Design
* Divide large scale codes to multiple level function calls.
* Design functions with high input fans and low output fans
* Write re-entrant function as much as possible
* Define only one logic task for each function as much as possible
* Keep the length of each function within 200~300 lines
* Separate implemention codes from control codes

Physical Structure of Code
* The basic code unit is a set of files, c/cpp file and its associated h files which might be more than one, like one for the public and another one for the private. The c/cpp file in one unit is supposed to include its h files.
* The h files should include non-std h files as few as possible. These non-std h files should be included in the c/cpp file. The h files could do forward declarations for type declarations within itself in its beginning to avoid including other h files.
* Each h file should be guarded with #ifndef/#define and its unique tag.
* Avoid using `extern' functions directly in c/cpp file but try to include the h files of their declarations.
* Use `static' to restrict the scope of functions and variables. Global variables should be `extern' declared in its h file and defined & initialized in the c/cpp files. Include the h file of global variables first before use them.

Misc
* Not do too much in ONE single statement.
* malloc and free
- Check the return pointer of malloc, reset the memory allocated to zeros with memset.
- Free the memory allocated by malloc at the same code level, assign NULL to the pointer finally.
* fopen and fclose
- Check the return handle of fopen
- Close the file handle in the end
* sizeof and size_t
- size_t == unsigned long int
- sizeof data type instead of variable name
- Prefer (num * sizeof data type) to (sizeof data type * num)
* Condition Check with Boolean, Int, Float and Pointer
- Boolean: if (!Flag)
- Int: if (0 == Flag)
- Float: if (Flag >= -EPSILON && Flag <= EPSILON)
- Pointer: if (NULL == p)
* Infinite Loop - while (1) {...}