Enumeration (or enum) is a user defined data type in C. It is mainly used to assign names to integral constants, the names make a program easy to read and maintain.
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The keyword ‘enum’ is used to declare new enumeration types in C and C++. Following is an example of enum declaration.
Variables of type enum can also be defined. They can be defined in two ways:
// of enum in C { day = Wed; return0; |
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 of enumeration is:
// Another example program to demonstrate working #include<stdio.h> enumyear{Jan, Feb, Mar, Apr, May, Jun, Jul, { for(i=Jan; i<=Dec; i++) } |
Output:
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 facts about initialization of enum.
1. Two enum names can have same value. For example, in the following C program both ‘Failed’ and ‘Freezed’ have same value 0.
enumState {Working = 1, Failed = 0, Freezed = 0}; intmain() printf('%d, %d, %d', Working, Failed, Freezed); } |
Output:
2. 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.
C++ Enum Naming
enumday {sunday, monday, tuesday, wednesday, thursday, friday, saturday}; intmain() enumday d = thursday; printf('The day number stored in d is %d', d); } |
Output:
3. We can assign values to some name in any order. All unassigned names get value as value of previous name plus one.
enumday {sunday = 1, monday, tuesday = 5, wednesday, thursday = 10, friday, saturday}; intmain() printf('%d %d %d %d %d %d %d', sunday, monday, tuesday, wednesday, thursday, friday, saturday); } |
Output:
4. 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.
5. All enum constants must be unique in their scope. For example, the following program fails in compilation.
enumresult {failed, passed}; intmain() { return0; } |
Output:
Exercise:
Predict the output of following C programs
Program 1:
enumday {sunday = 1, tuesday, wednesday, thursday, friday, saturday}; intmain() enumday d = thursday; printf('The day number stored in d is %d', d); } |
Program 2:
enumState {WORKING = 0, FAILED, FREEZED}; returncurrState; (FindState() WORKING)? printf('WORKING'): printf('NOT WORKING'); } |
Enum vs Macro
We can also use macros to define names constants. For example we can define ‘Working’ and ‘Failed’ using following macro.
#define Failed 1 |
There are multiple advantages of using enum over macro when many related named constants have integral values.
a) Enums follow scope rules.
b) Enum variables are automatically assigned values. Following is simpler
C++ Enum Count
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An enumerated type is a distinct type whose value is a value of its underlying type (see below), which includes the values of explicitly named constants (enumeration constants).
[edit]Syntax
Enumerated type is declared using the following enumeration specifier as the type-specifier in the declaration grammar:
enumattr-spec-seq(optional)identifier(optional){enumerator-list} |
where enumerator-list is a comma-separated list (with trailing comma permitted)(since C99) of enumerator, each of which has the form:
| enumeration-constantattr-spec-seq(optional) | (1) |
enumeration-constantattr-spec-seq(optional)=constant-expression | (2) |
where
| identifier, enumeration-constant | - | identifiers that are introduced by this declaration |
| constant-expression | - | integer constant expression whose value is representable as a value of type int |
| attr-spec-seq | - | (C23)optional list of attributes,
|
As with struct or union, a declaration that introduced an enumerated type and one or more enumeration constants may also declare one or more objects of that type or type derived from it.
[edit]Explanation
Each enumeration-constant that appears in the body of an enumeration specifier becomes an integer constant with type int in the enclosing scope and can be used whenever integer constants are required (e.g. as a case label or as a non-VLA array size).
If enumeration-constant is followed by = constant-expression, its value is the value of that constant expression. If enumeration-constant is not followed by = constant-expression, its value is the value one greater than the value of the previous enumerator in the same enumeration. The value of the first enumerator (if it does not use = constant-expression) is zero.
The identifier itself, if used, becomes the name of the enumerated type in the tags name space and requires the use of the keyword enum (unless typedef'd into the ordinary name space).
Each enumerated type is compatible with one of: char, a signed integer type, or an unsigned integer type. It is implementation-defined which type is compatible with any given enumerated type, but whatever it is, it must be capable of representing all enumerator values of that enumeration.
Enumerated types are integer types, and as such can be used anywhere other integer types can, including in implicit conversions and arithmetic operators.
[edit]Notes
Unlike struct or union, there are no forward-declared enums in C:
Enumerations permit the declaration of named constants in a more convenient and structuredfashion than does #define; they are visible in the debugger, obey scope rules, and participate in the type system.
or
Moreover, as a struct or union does not establish its scope in C, an enumeration type and its enumeration constants may be introduced in the member specification of the former, and their scope is the same as of the former, afterwards.
[edit]Example
Output:
[edit]References
- C17 standard (ISO/IEC 9899:2018):
- 6.2.5/16 Types (p: 32)
C++ Enum
- 6.7.2.2 Enumeration specifiers (p: 84-85)
C++ Enum Class Int
- C11 standard (ISO/IEC 9899:2011):
- 6.2.5/16 Types (p: 41)
- 6.7.2.2 Enumeration specifiers (p: 117-118)
- C99 standard (ISO/IEC 9899:1999):
- 6.2.5/16 Types (p: 35)
- 6.7.2.2 Enumeration specifiers (p: 105-106)
- C89/C90 standard (ISO/IEC 9899:1990):
- 3.1.2.5 Types
C Game Dev Enumerated
- 3.5.2.2 Enumeration specifiers
[edit]Keywords
[edit]See also