(1) #define a macro definition command (allowing C or C ++ source code used in an identifier to indicate a character string called "macro")
Identifier: it means a symbol used to identify an entity
When the preprocessor replaced
例：#define PI 3.141592653
(Identifier) (String)
S = PI * r * r;
The PI 3.141592653 replaced when the preprocessor.
(2) typedef (declared type, keyword)
When used with the structure struct, the format:
typedef struct{
......
} Dog;
The complex is defined as a statement alias , the purpose of the source code easier to read and understand.
The structure is struct {.......} this section, with "dog" indicates, when used in the structure, the direct use of a "dog" can represent a large segment of code structure.
Supplementary: ① Note: #define last no semicolon;
② # parameters used to convert into a string;
## is used to connect the front and rear two parameters, turning them into a string
③ structure struct definition:
struct 结构名
{
//成员表列，就是数据集合
};