enum in C

Enumeration (enum) is a user-defined datatype (same as structure). It consists of various elements of that type. There is no such specific use of enum, we use it just to make our codes neat and more readable. We can write C programs without using enumerations also.

For example, Summer, Spring, Winter and Autumn are the names of four seasons. Thus, we can say that these are of types season. Therefore, this becomes an enumeration with name season and Summer, Spring, Winter and Autumn as its elements.

So, you are clear with the basic idea of enum. Now let's see how to define it.

Defining an Enum

An enum is defined in the same way as structure with the keyword struct replaced by the keyword enum and the elements separated by 'comma' as follows.

enum enum_name
{
  element1,
  element2,
  element3,
  element4,
};

Now let's define an enum of the above example of seasons.

Here, we have defined an enum with name 'season' and 'Summer, Spring, Winter and Autumn' as its elements.

Declaration of Enum Variable

We also declare an enum variable in the same way as that of structures. We create an enum variable as follows.

So, here 's' is the variable of the enum named season. This variable will represent a season. We can also declare an enum variable as follows.

Values of the Members of Enum

All the elements of an enum have a value. By default, the value of the first element is 0, that of the second element is 1 and so on.

Let's see an example.

#include <stdio.h>
enum season{ Summer, Spring, Winter, Autumn};
int main()
{
    enum season s;
    s = Spring;
    printf("%d\n",s);
    return 0;
}

Here, first we defined an enum named 'season' and declared its variable 's' in the main function as we have seen before. The values of Summer, Spring, Winter and Autumn are 0, 1, 2 and 3 respectively. So, by writing s = Spring, we assigned a value '1' to the variable 's' since the value of 'Spring' is 1.

We can also change the default value and assign any value of our choice to an element of enum. Once we change the default value of any enum element, then the values of all the elements after it will also be changed accordingly. An example will make this point clearer.

#include <stdio.h>
enum days{ sun, mon, tue = 5, wed, thurs, fri, sat};
int main()
{
    enum days day;
    day = thurs;
    printf("%d\n",day);
    return 0;
}

The default value of 'sun' will be 0, 'mon' will be 1, 'tue' will be 2 and so on. In the above example, we defined the value of tue as 5. So the values of 'wed', 'thurs', 'fri' and 'sat' will become 6, 7, 8 and 9 respectively. There will be no effect on the values of sun and mon which will remain 0 and 1 respectively. Thus the value of thurs i.e. 7 will get printed.

Let's see one more example of enum.

#include <stdio.h>
enum days{ sun, mon, tue, wed, thurs, fri, sat};
int main()
{
    enum days day;
    day = thurs;
    printf("%d\n",day+2);
    return 0;
}

In this example, the value of 'thurs' i.e. 4 is assigned to the variable day. Since we are printing 'day+2' i.e. 6 (=4+2), so the output will be 6.