C++ Enumeration

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

enum season { spring, summer, autumn, winter };

Here, the name of the enumeration is season.

And, spring, summer and winter are values of type season.

By default, spring is 0, summer is 1 and so on. You can change the default value of an enum element during declaration (if necessary).

enum season 
{   spring = 0, 
    summer = 4, 
    autumn = 8,
    winter = 12
};

Enumerated Type Declaration

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

enum boolean { false, true };

// inside function
enum boolean check;

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

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

enum boolean 
{ 
   false, true
} check;

Example: Enumeration Type

#include <iostream>
using namespace std;

enum week { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };

int main()
{
    week today;
    today = Wednesday;
    cout << "Day " << today+1;
    return 0;
}

Output

Day 4

Example: Changing Default Value of Enums

#include <iostream>
using namespace std;

enum seasons { spring = 34, summer = 4, autumn = 9, winter = 32};

int main() {

    seasons s;

    s = summer;
    cout << "Summer = " << s << endl;

    return 0;
}

Output

Summer = 4

Why are enums used in C++ programming?

An enum variable takes only one value out of many possible values. Let us look at an example.

#include <iostream>
using namespace std;

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

int main() 
{
    card = club;
    cout << "Size of enum variable " << sizeof(card) << " bytes.";   
    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 C++ structures. However, working with enums gives you efficiency along with flexibility.

How to use enums for flags?

Let us look at an example.

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

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

There is a reason why all the integral constants are powers of 2 in the 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 <iostream>
using namespace std;

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

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

        //    00000010
        //  | 00000100
        //  ___________
        //    00000110

    cout << myDesign;

    return 0;
}

Output

6

When the output is 6, you always know that BOLD and UNDERLINE are used.

Also, you can add flags 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 the 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.