Rough notes of C language (2) -- constants

Constant

C The definition forms of constants and variables in language are different .
C Language constants are divided into the following ：

1. Literal constants
2. Const Modified constant variable
3. #define Defined identifier constant
4. Enumeration constants

 Literal constants

For example, you can call directly “1” Nothing else, just literally

 Const Modified constant variable

Const int num=4
Num by Const Modified constant variable , Has constant properties , Have constant characteristics and —— Can't change , But it's essentially a variable .

The above is a simple example to help understand , When const modification num Make it a constant variable , If you assign a value to it , Will report a mistake , because num Is already a constant variable , And have constant properties , Its value cannot be changed , But to be clear, its essence is variables .
The essential proof is that the variables are as follows ：
So let's define one const Modified constant variable num. Then write it into the array

At this time, the subscript in the mapping array is 0 Then you will find that it reports an error , And in brackets , I want you to fill in the constant , At this time, we lose const Embellished num, shows num Is not a constant .

The value in the middle bracket is changed to a literal constant 8 Timely and successful .
Therefore, we should also know that the array is determining its size “【】” What should be written in brackets is a constant . When can variables be used in the brackets of an array ？
When you represent one of the arrays , Variables can be used in brackets to represent the subscript of the array .
as follows ：

 #define Defined identifier constant

 Enumeration constants

Enumerate and enumerate one by one
Enumerate keywords enum

Each enumeration constant （ Here it means small,middle,big） There is a corresponding fixed value . So they are called “ Enumeration constants ” It can also be understood as taking a name , That name is essentially equivalent to a number .
The following helps understand ： Define a variable created by enumeration s, Make it equal to small. And equal to s=0;

Variables created by enumeration types can be changed , But enumeration constants cannot be changed .
Um. ？？？？？ What do you mean by that? ？？？？？？？
 Variables created by enumeration types can be changed

 But enumeration constants cannot be changed

Small It is already an enumeration constant , You can't say that you can assign it again as a variable .