NOTE

1. limits.h头文件中包含了关于此编译器实现的c数据类型的定义。
2. 使用转义字符的时候，可以使用'\'，'\0xxx'(0可以省略)，'\0xxxx'
3. the difference of using sizeof array when main and  using sizeof array when function
4. you can legally access the address of the array's last address + 1.
5. the difference of const point and point const
	const int * pt;	//this is a pointer --> a const value, but the value of pt can change
	int * const pt; //this is a const pointer --> a variable, but the value of pt cannot change
	const int * const pt;//this is a const pointer --> a const value, you cannot change either the value of pt nor the value of pt --> value
6. the difference of "int * pz[2]" and "int (*pz) [2]"
	int * pz[2] --> int * is the array's type
	int (*pz) [2] --> pz is a pointer to two dimensions's array 
7. fgets(char* , int MAX, FILE* )
	the difference between gets is that fgets can read the '\n' and add '\0' to the end, but the gets will replace the '\n' with '\0'
8. fgets and fputs
   gets and puts
   getchar and putchar
   getc and putc