Enumeration in C++

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Enumeration (or enum) is a user defined data type in C and C++. It is mainly used to assign names to integral constants, the names make a program easy to read and maintain.

C++ allows programmer to define their own function.A user-defined function groups code to perform a specific task and that group of code is given a name(identifier).
When the function is invoked from any part of program, it all executes the codes defined in the body of function.

Synatx :

enum enum_name{constant1, constant2, constant3, ....... };

NOTE : Like in array we have index number here also the constant have index number.

Examples

An example program to demonstrate working of enum in C++

#include<iostream.h> 
  
enum week{Mon, Tue, Wed, Thur, Fri, Sat, Sun}; 
int main() 
{ 
    enum week day; //calling enum
    day = Wed; 
    cout<<day; 
    return 0; 
}

Output :

In the above example, we declared “day” as the variable and the value of “Wed” is allocated to day, which is 2. So as a result, 2 is printed.

Another example program to demonstrate working of enum in C++

#include<iostream.h> 
enum year{Jan, Feb, Mar, Apr, May, Jun, Jul,Aug, Sep, Oct, Nov, Dec}; 
int main() 
{ 
   int i; 
   for (i=Jan; i<=Dec; i++)       
      printf("%d ", i); 
        
   return 0; 
}

Output :

0 1 2 3 4 5 6 7 8 9 10 11

In this example, the for loop will run from i = 0 to i = 11, as initially the value of i is Jan which is 0 and the value of Dec is 11.

Interesting fact about enum

Two enum names can have same value. For example, in the following C program both ‘Failed’ and ‘Freezed’ have same value 0.

#include <iostream.h> 
enum State {Work = 1, Fail = 0, Freez = 0}; 
  
int main() 
{ 
   cout<<Work<<Fail<<Freez; 
   return 0; 
}

Output :

1, 0, 0

If we do not explicitly assign values to enum names, the compiler by default assigns values starting from 0.
For example, in the following C++ program, sunday gets value 0, monday gets 1, and so on.

#include <iostream.h> 
enum day {sunday, monday, tuesday, wednesday, thursday, friday, saturday}; 
  
int main() 
{ 
    enum day d = thursday; 
    cout<<"The day number stored in d is :"<<d; 
    return 0; 
}

Output:

The day number stored in d is : 4

We can assign values to some name in any order. All unassigned names get value as value of previous name plus one.

#include <iostream.h> 
enum day {sunday = 1, monday, tuesday = 5,wednesday, thursday = 10, friday, saturday}; 
  
int main() 
{ 
    cout<<sunday<<monday<<tuesday<<wednesday<<thursday<<friday<<saturday; 
    return 0; 
}

Output :

1 2 5 6 10 11 12

The value assigned to enum names must be some integeral constant, i.e., the value must be in range from minimum possible integer value to maximum possible integer value.
All enum constants must be unique in their scope. For example, the following program fails in compilation.

enum state  {working, failed}; 
enum result {failed, passed}; 
  
int main()  
{
    return 0; 
}

Output :

Compile Error: 'failed' has a previous declaration as 'state failed'

Question

Which variable has equal size with enum variable?

int variable

float variable

string variable

none of the mentioned

The enum variable is converted to an integer and stored by the compiler. So both are equal in size.