Constant knowledge explanation of C language

Constant

C Language includes Constant and Variable , Let's talk about it today C Constant in language .

Constants are divided into the following ：

（1） Literal constants ： Usually written directly Invariant quantity （ It can be an integer , Floating point numbers , character , character string ）

#include<stdio.h>
int main()
{
123456;  // Literal constants 
5.21;    // Literal constants 
‘a’;     // Literal constants 
"abcd";  // Literal constants 
return 0;
}

(2）const Embellished Constant variable （ As the name suggests, it has the characteristics of variables, but it is still a constant ）

#include<stdio.h>
int main()
{
const int a = 5;
a = 6;// here a The value of will not change ,a Is a variable but in const Under the decoration of ,a The value of determines , Cannot change , For constant .
int m[a] = {0,1,2,3};//a Here we have the properties of variables , This is the wrong expression definition array in some compilers 
}

（3）#define Defined Identifier constant （ Macro definition , Define before the main function ）

#include<stdio.h>
#define PI 3.14
#define MAX 10
int main()
{
int a = 0;
a = PI*PI;         //PI The value of can be directly used 
int arr[MAX] = {0};//MAX It's a constant 10
printf("%d",a);
printf("%d",arr[1]);
return 0;
}

（4） Enumeration constants （ There is a fixed format , Common in general life Gender , Three primary colors And so on , You can use enumeration ）

enum SEX   // Gender can be divided into men and women   It can be counted 
{
   nan,    // Enumerating combinations of constants   here nan  The default is 0, first （nv Or in the first ）
   nv      // The default is 1
};
int main()
{
    printf("%d\n", nan); // Output is 0
	printf("%d\n", nv);  // Output is 1
	return 0;

}

That's all C The constant knowledge of language is explained .

Ask for three company , Pay attention ！