C Programming Enumeration

In this article, you will learn to work with enumeration (enum). Also, you will learn where enums are commonly used in C programming.
C enum

An enumeration is a user-defined data type that consists of integral constants. To define an enumeration, keyword enum is used.

enum flag { const1, const2, ..., constN };

Here, name of the enumeration is flag.

And, const1, const2,...., constN are values of type flag.

By default, const1 is 0, const2  is 1 and so on. You can change default values of enum elements during declaration (if necessary).

// Changing default values of enum
enum suit {
    club = 0,
    diamonds = 10,
    hearts = 20,
    spades = 3,
};

Enumerated Type Declaration

When you create an enumerated type, only blueprint for the variable is created. Here's how you can create variables of enum type.

enum boolean { false, true };
enum boolean check;

Here, a variable check of type enum boolean is created.

Here is another way to declare same check variable using different syntax.

enum boolean 
{ 
   false, true
} check;

Example: Enumeration Type

#include <stdio.h>

enum week { sunday, monday, tuesday, wednesday, thursday, friday, saturday };

int main()
{
    enum week today;
    today = wednesday;
    printf("Day %d",today+1);
    return 0;
}

Output

Day 4

Why enums are used in C programming?

Enum variable takes only one value out of many possible values. Example to demonstrate it,

#include <stdio.h>

enum suit {
    club = 0,
    diamonds = 10,
    hearts = 20,
    spades = 3
} card;

int main() 
{
        card = club;
	printf("Size of enum variable = %d bytes", sizeof(card));	
	return 0;
}

Output

Size of enum variable = 4 bytes

It's because the size of an integer is 4 bytes. 

This makes enum a good choice to work with flags.

You can accomplish the same task using structures. However, working with enums gives you efficiency along with flexibility.

How to use enums for flags?

Let us take an example,

enum designFlags {
	ITALICS = 1,
	BOLD = 2,
	UNDERLINE = 4
} button;

Suppose you are designing a button for Windows application. You can set flags ITALICS, BOLD and UNDERLINE to work with text.

There is a reason why all the integral constants are power of 2 in above pseudocode.

// In binary

ITALICS = 00000001
BOLD = 00000010
UNDERLINE = 00000100 

Since, the integral constants are power of 2, you can combine two or more flags at once without overlapping using bitwise OR | operator. This allows you to choose two or more flags at once. For example,

#include <stdio.h>

enum designFlags {
	BOLD = 1,
	ITALICS = 2,
	UNDERLINE = 4
};

int main() {
	int myDesign = BOLD | UNDERLINE; 

        //    00000001
        //  | 00000100
        //  ___________
        //    00000101

	printf("%d", myDesign);

	return 0;
}

Output

5

When the output is 5, you always know that bold and underline is used.

Also, you can add flag to your requirements.

if (myDesign & ITALICS) {
    // code for italics
}

Here, we have added italics to our design. Note, only code for italics is written inside if statement.

You can accomplish almost anything in C programming without using enumerations. However, they can be pretty handy in certain situations. That's what differentiates good programmers from great programmers.