Enumerated types allow a set of named integer constants to be defined. An enumeration type declaration specifies the enumeration tag name and defines the enumerator constants. A variable of an enum type can only hold one of the defined enumerator constant values. Enumerations provide an alternative to #define with advantages like automatically generated values and normal scoping rules. Typedef allows custom type names to be defined as synonyms for existing types like int, float, and double without reserving new storage. Typedef names exist in the same namespace as other identifiers except for variably modified types which have block scope.

1. ENUMERATED, typedef

2. ENUMERATED DATA TYPES
• An enumeration consists of a set of named integer
constants.
• An enumeration type declaration gives the name of the
(optional) enumeration tag and defines the set of named
integer identifiers (called the "enumeration set,"
"enumerator constants," "enumerators," or "members").
A variable with enumeration type stores one of the
values of the enumeration set defined by that type.
• Variables of enum type can be used in indexing
expressions and as operands of all arithmetic and
relational operators.
• Enumerations provide an alternative to the #define
preprocessor directive with the advantages that the
values can be generated for you and obey normal
scoping rules.

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ENUMERATED DATA TYPES
enum identifier { enumerator-list }
Example
#include <stdio.h>
#include <conio.h>
#include <alloc.h>
void main()
{
clrscr();
enum month { jan = 1, feb, mar, apr, may, jun, jul,
aug, sep, oct, nov, dec };
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printf("%d“,feb);
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getch();
• }

4. typedef
• A typedef declaration lets you define your own
identifiers that can be used in place of type specifiers
such as int, float, and double.
• A typedef declaration does not reserve storage.
• The names you define using typedef are not new data
types, but synonyms for the data types or combinations
of data types they represent.
• The name space for a typedef name is the same as other
identifiers.
• The exception to this rule is if the typedef name
specifies a variably modified type. In this case, it has
block scope.
• typedef int LENGTH;
• LENGTH length, width, height;