constant symbolization

In programs, we often avoid numbers appearing directly and replace them with specific words or other strings that can express meaning, which can greatly improve readability.
For example, using words instead of numbers

enumerate

Concept explanation

Enumeration is a user-defined data type, which is declared with the keyword enum. To define an enumeration is to assign names to some constants : enum enumeration name {name 0, name 1,..., name n}; can also be Specify value (enumeration)
Most of the time the enumeration name is omitted when used, because it is not really used, and the name in brackets is more important .
The brackets are actually constant symbols, the type is int , and the values increase from 0 to n.

Program example

#include <stdio. h>
enum color { red, yellow, green};
 
//枚举类型要跟上enum，无论是函数的参数表里还是变量里（C语言中规定）
//这里是函数参数表
void f(enum color c);
 
 
int main(void)
{
//枚举量可以作为值
    enum color t = red;
 
//实际上，red就是0，C语言内部以整数来处理它
    scanf("%d", &t);
    f(t);
    return 0;
}
void f(enum color c)
{
    printf("%d\n"，c);
}

Input/output/2 2/ 3 3/ 55 55

Enumerators can be used as values
Enumeration types can follow enum as type
But in fact, integers are used for internal calculations and external output.

A little trick: automatic counting of enumerations

The internal counting rules of enumerations are the same as those of arrays, counting starts from 0, so if a name is added to the end of the element, the number represented by the name is the count of the previous name .
For example, enum color { red, yellow, green, NumColors}; //NumColors represents 3, with exactly 3 elements in front

At this time, if you need to traverse all enumerations, or if you need to create an array with enumerations as subscripts, you can easily know the number of enumerations .

#include <stdio.h>
enum COLOR {RED，YELLOW， GREEN, NumCOLORS};
 
int main(int argc, char const *argv[])
{
    int color = -1;
//可以用NumColors建立数组
    char *ColorNames [NumCOLORS] = {
    "red", "yellow", "green",
    };
    char *colorName = NULL;
 
    printf("输入你喜欢的颜色的代码: ");
    scanf("%d", &color);
//可以用NumColors作为判断依据
    if ( color >=0 && color < NumCOLORS ) {
    colorName = ColorNames [color] ;
    } else {
    colorName= "unknown" ;
    }
 
    printf ("你喜欢的颜色是%s\n"，colorName);
    return 0;
}

char *ColorNames [NumCOLORS] = {
"red", "yellow", "green", };

string array

enumerator

When declaring an enumeration, you can not follow the default principle and customize the value.

enum COLOR {RED=1，YELLOW， GREEN=5 };
//此时yellow=2

The enumerator is only of type int (but assigning an integer exceeding int to the enumerator will not cause an error , or 0)
Although enumeration types can be used as types, they are not easy to use. . .
For names that are comparable in meaning, it is more convenient to use enumerations than const int , and there is no need to write them line by line.
Enumerations are better than macros because enumerations have int type and macros have no type.
The main purpose of enumerations is to define some symbolic quantities, rather than as a type

C language_0328 notes_enumeration: constant symbolization/int value/custom enumeration/automatic enumeration counting/not very commonly used