What is an enumeration (enum) in C?

An Enumeration or enum, is a user-defined data structure in C. Enumerations allow users to assign names to integer constants. Let’s take a deeper look:

Example

In this example, we will be considering the days of the week from Sunday to Saturday to create an enumeration.

Here’s the syntax:

enum week_days = {Sun, Mon, Tue, Wed, Thu, Fri, Sat};

enum week_days day;

We’ve created an enumeration of the days of the week.

  • The enum is declared within the variable week_days
  • The variable day is an object of our enum type variable and can be used to store the associated integer constant of our week_days elements

Since we did not assign specific integer values to each name ourselves, the compiler assigns values starting from 0.

Code

We will now be looking at different ways to use an enumeration.

1. Basic

#include<stdio.h>
//Global enum
enum week_days {Sun, Mon, Tue, Wed, Thu, Fri, Sat};
//              0,   1,   2,   3,   4,   5,   6
int main() {
  
  enum week_days today;
  today = Fri;
  printf("Today is the %dth day of the week!", today);
  
  return 0;
}

2. Iterator

#include<stdio.h>
enum week_days {Sun, Mon, Tue, Wed, Thu, Fri, Sat};
int main() {
    int i;
    for(i = Sun; i <= Sat; i++)
        printf("%d\n", i);
    return 0;
}

Keep in mind

Enumerations can make our code easy to read and comprehend. Let’s do a quick recap of what we’ve learned and discuss key enum functionalities:

  1. enum assigns names to integer constants.

  2. If an integer is not associated with any name within the enum, the compilers will assign values starting from 0.

  3. We can assign specific values ourselves as well. The names that we choose not to assign will automatically be assigned the value of its predecessor, + 1.

#include <stdio.h>
enum assignment_example{just = 1, an, example = 4};
int main() {
  
  printf("%d\n", an);
  
  //Expect '2' as an output as the predecessor on 'an' is
  //'just' with an assigned value of '1'
  return 0;
}

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