Simple Enumeration

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An enumeration is a user-defined data type consists of integral constants and each integral constant is given a name. Keyword enum is used to define enumerated data type.

If you use enum instead of int or string/ char*, you increase compile-time checking and avoid errors from passing in invalid constants, and you document which values are legal to use.

Example 1

enum color{ RED, GREEN, BLUE };

void printColor(enum color chosenColor)
{
    const char *color_name = "Invalid color";
    switch (chosenColor)
    {
       case RED:
         color_name = "RED";
         break;
       
       case GREEN:
        color_name = "GREEN";
        break;    

       case BLUE:
        color_name = "BLUE";
        break;
    }
    printf("%s\n", color_name);
}

With a main function defined as follows (for example):

int main(){
    enum color chosenColor;
    printf("Enter a number between 0 and 2");
    scanf("%d", (int*)&chosenColor);
    printColor(chosenColor);
    return 0;
}

Example 2

(This example uses designated initializers which are standardized since C99.)

enum week{ MON, TUE, WED, THU, FRI, SAT, SUN };
     
static const char* const dow[] = { 
  [MON] = "Mon", [TUE] = "Tue", [WED] = "Wed", 
  [THU] = "Thu", [FRI] = "Fri", [SAT] = "Sat", [SUN] = "Sun" };
    
void printDayOfWeek(enum week day) 
{ 
   printf("%s\n", dow[day]);
}

The same example using range checking:

enum week{ DOW_INVALID = -1, 
  MON, TUE, WED, THU, FRI, SAT, SUN, 
  DOW_MAX };
     
static const char* const dow[] = { 
  [MON] = "Mon", [TUE] = "Tue", [WED] = "Wed", 
  [THU] = "Thu", [FRI] = "Fri", [SAT] = "Sat", [SUN] = "Sun" };
    
void printDayOfWeek(enum week day) 
{ 
   assert(day > DOW_INVALID && day < DOW_MAX);
   printf("%s\n", dow[day]);
}

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