Custom types: Enumeration

3. enumeration

Enumeration, as the name suggests, is to enumerate one by one
List the possible values one by one
For example, in our life ：

A week's Monday to Sunday is limited 7 God , You can list them one by one
Gender ： male , Woman , A secret , You can also list them one by one
Month has 12 Months , You can also list them one by one

These can be enumerated

3.1 Definition of enumeration type

enum Day// week 
{
    
	Mon,
	Tues,
	Wed,
	Thur,
	Fri,
	Sat,
	Sun
};
enum Sex// Gender 
{
    
	MALE,
	FEMALE,
	SECRET
};
enum Color// Color 
{
    
	RED,
	GREEN,
	BLUE
};

As defined above enum Day,enum Sex,enum Color All enumeration types .
{ } The contents in are possible values of enumeration types , Also called Enumeration constants .
These constants have not been stored in memory （ It is now a type , Is a drawing , Do not occupy memory ）, Only when they are assigned to some variables will they be stored in memory , Such as ：enum Day d = Fri;
Be careful ：
Enumeration constants have values , The default from the 0 Start , In turn, increasing 1, Such as ：

#include <stdio.h>
enum Day
{
    
	Mon,
	Tues,
	Wed,
	Thur,
	Fri,
	Sat,
	Sun
};

int main()
{
    
	printf("%d\n", Mon);
	printf("%d\n", Tues);
	printf("%d\n", Wed);
	printf("%d\n", Thur);
	printf("%d\n", Fri);
	printf("%d\n", Sat);
	printf("%d\n", Sun);
	return 0;
}

Of course, initial values can also be assigned when defining
for example ：

enum Color// Color 
{
    
 RED=1,
 GREEN=2,
 BLUE=4
};

3.2 Advantages of enumeration

Why use enumeration ？
We can use #define Define constants , Why do I have to use enumeration ？
Advantages of enumeration ：

1. Increase the readability and maintainability of the code
2. and #define Defined identifier , Enumeration type checking is more rigorous
3. Prevent named pollution （ encapsulation ）
4. Easy to debug
5. Easy to use , You can define more than one constant at a time

3.3 Use of enumeration

enum Color// Color 
{
    
 RED=1,
 GREEN=2,
 BLUE=4
};
enum Color clr = GREEN;// Only enumeration constants can be assigned to enumeration variables , There will be no type difference .
clr = 5;               //ok??

The above code is in C The program can run , stay C++ Not in grammar . Because enumeration is a type , stay C++ In grammar , You can't put one int Type is assigned to enumeration type .