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 c++-enum

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What is Enumeration in C++

  • 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).
  • learn c++ tutorials - enum in c++

    learn c++ tutorials - enum in c++ Example

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

// inside function
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 1: 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
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Example2: 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
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Why enums are used in C++ programming?

  • An enum variable takes only one value out of many possible values.

Example to demonstrate it,

#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 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 <iostream>
using namespace std;

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

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

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

    cout << myDesign;

    return 0;
}
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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
}

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