User-Defined Data Types

C++ is a flexible language, it allows user to define their own data types. User can do this with a keyword typedef. Format to declare a user defined data type is:

                     typedef existing_type new_type_name

          In above format existing_type
indicate the standard data types of C++ and new_type_name shows the data
type name defined by the user. for example, if:

• typedef char C
• typedef unsigned int U
• typedef char box [30]

           In this case we defined three
data types: C, U, and field as char, unsigned int, and char[30]
respectively, that we could perfectly use in declarations later as any
other valid type:

• C ultra, fest,mob;
• U nin;
• box name;

            typedef does not create
different types. It only creates synonyms of existing types. That means
that the type of nin can be either U or unsigned int, since both are in
fact the same type. typedef can be useful to define an alias for a type
that is frequently used within a program. It is also useful to define
types when it is possible that we will need to change the type in later
versions of our program, or if a type you want to use has a name that is
too long or confusing.

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