The difference between a define and a typedef defined by a macro

1) #define是预处理指令, in the compilation preprocessing simple substitution, does not make the correctness check, does not have the meaning whether correctly still brings in, only when compiles the already expanded source program only then discovers the possible error and error. For example:
#define PI 3.1415926
In the program: Area=pi*r*r will be replaced with 3.1415926*r*r
If you write the number 9 in the # define statement as the letter G preprocessing is also brought in.

#define is not a statement do not add a semicolon at the end of the line, or a semicolon is replaced.

2) A typedef is processed at compile time. It gives an alias to an already existing type within its scope, but you cannot use the typedef specifier inside a function definition.

The difference between a define and a typedef defined by a macro