- Enumeration:
- An enumeration consists of a set of named integer constants.
Example:
- Sunday = 0
- Monday = 1
- Tuesday = 2
- Wednesday = 3
- Thursday = 4
- Friday = 5
- Saturday = 6
- Enumeration data type:
- An enumeration type declaration
specifies:
- the (optional) enumeration set name
- a list of named integer identifiers (called the "enumeration set," "enumerator constants," "enumerators," or "members")
- An enumeration type declaration
specifies:
- Example: we can define the
above enumeration using
the following
enumeration type declaration:
enum Day { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };
- Example program:
/* ------------------------ Emumeration declaration ------------------------ */ enum Day { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }; int main(int argc, char *argv[]) { printf("Sunday = %d\n", Sunday ); printf("Monday= %d\n", Monday ); printf("Tuesday = %d\n", Tuesday ); printf("Wednesday = %d\n", Wednesday ); printf("Thursday = %d\n", Thursday ); printf("Friday = %d\n", Friday ); printf("Saturday = %d\n", Saturday ); }Output:
Sunday = 0 Monday= 1 Tuesday = 2 Wednesday = 3 Thursday = 4 Friday = 5 Saturday = 6
- Facts about the
enumeration data type:
- By default, the
first identifier in
the enumeration list is assigned with the
value 0 (ZERO)
- You can override the default
value by specifiying a
specific value with the syntax:
identifier = value
- You can override the default
value by specifiying a
specific value with the syntax:
- Each subsequent identifier is
assigned with the
value equal to
1 greater than the previous value,
unless:
- you specify a specific value for that identifier
- By default, the
first identifier in
the enumeration list is assigned with the
value 0 (ZERO)
- Example 1: starting with a
non-zero initial value
- Test program:
enum Day { Sunday = -1, // initial value Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }; int main(int argc, char *argv[]) { printf("Sunday = %d\n", Sunday ); printf("Monday= %d\n", Monday ); printf("Tuesday = %d\n", Tuesday ); printf("Wednesday = %d\n", Wednesday ); printf("Thursday = %d\n", Thursday ); printf("Friday = %d\n", Friday ); printf("Saturday = %d\n", Saturday ); }Output:
Sunday = -1 Monday= 0 Tuesday = 1 Wednesday = 2 (Values increases by 1) Thursday = 3 Friday = 4 Saturday = 5
- Test program:
- Example 2:
repeating values are
possible !!!
- Test program:
enum Day { Sunday, // Default 0 Monday, // 1 Tuesday, // 2 Wednesday = 0, // Forced to 0 Thursday, // 1 again !! Friday, // 2 Saturday // 3 }; int main(int argc, char *argv[]) { printf("Sunday = %d\n", Sunday ); printf("Monday= %d\n", Monday ); printf("Tuesday = %d\n", Tuesday ); printf("Wednesday = %d\n", Wednesday ); printf("Thursday = %d\n", Thursday ); printf("Friday = %d\n", Friday ); printf("Saturday = %d\n", Saturday ); }Output:
Sunday = 0 Monday= 1 Tuesday = 2 Wednesday = 0 Thursday = 1 Friday = 2 Saturday = 3
- Test program:
- Example Program:
(Demo above code)
- Prog file: click here
How to run the program:
- Right click on link(s) and
save in a scratch directory
- To compile: gcc enum3.c
- To run: ./a.out
- enum typed variables:
- A variable of an enumeration type stores one of the values of the enumeration set defined by the enumeration type.
- Syntax to define a
variable of an
enumeration data type:
enum EnumTypeName varName ;
- How to use
variables of
an enumeration data type:
- Simple rule:
- You can use a variable of an enumeration data type anywhere you can use an integer value
- Examples:
- Value and
variables
of enum type can be used in:
- indexing expressions:
double a[10]; a[Sunday]
- operands of
all arithmetic
and relational operators:
Monday - Sunday
- indexing expressions:
- Value and
variables
of enum type can be used in:
- Simple rule:
- Example:
enum Day { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }; int main(int argc, char *argv[]) { enum Day today; // Define an enum typed variable today = Wednesday; printf("sizeof(today) = %d\n", sizeof(today) ); // Size = 4 (is an int variable !) printf("today = %d\n", today ); /* ================================ Note: no range check !!! ================================ */ today = 1000; // And out of range value, no error ! printf("an out of range value for today = %d\n", today ); }Output:
sizeof(today) = 4 today = 3 today = 1000
- Example Program:
(Demo above code)
- Prog file: click here
How to run the program:
- Right click on link(s) and
save in a scratch directory
- To compile: gcc enum4.c
- To run: ./a.out
- Fact:
- An enumeration type is just an integer type
Evidence:
enum Day { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }; enum boolean { false, true }; int main(int argc, char *argv[]) { enum Day x; enum boolean y = 44; int z = 444; x = 1; x = Monday; // No errors in all statements !!! x = true; x = y; x = z; }
- Example Program:
(Demo above code)
- Prog file: click here
How to run the program:
- Right click on link and
save in a scratch directory
- To compile: gcc type3.c
- To run: a.out
- You can enhance the
C programming language with the following
emueration data types to
make it more
user-friendly:
- Boolean type
enum BOOLEAN /* Declares an enumeration data type called BOOLEAN */ { false, /* false = 0, true = 1 */ true }; enum BOOLEAN done; // Boolean variable
- Boolean type
- Morale of the enum story:
- Enumerations
is equivaluent to
using a lot of #define
preprocessor directives to define the
symbolic constants.
- It has the advantage
that the values can be
generated automatically
(and with some care,
each value will also be unique)
- An enumeration typed variable is nothing more than an int variable !
- Enumerations
is equivaluent to
using a lot of #define
preprocessor directives to define the
symbolic constants.