User defined type declaration

In C language a user can define an identifier that represents an existing data type. The user defined datatype identifier can later be used to declare variables. The general syntax is

typedef type identifier;

here type represents existing data type and ‘identifier’ refers to the ‘row’ name given to the data type.

Example:

typedef int salary;
typedef float average;

Here salary symbolizes int and average symbolizes float. They can be later used to declare variables as follows:

Units dept1, dept2;
Average section1, section2;

Therefore dept1 and dept2 are indirectly declared as integer datatype and section1 and section2 are indirectly float data type.

The second type of user defined datatype is enumerated data type which is defined as follows.

Enum identifier {value1, value2 …. Value n};

The identifier is a user defined enumerated datatype which can be used to declare variables that have one of the values enclosed within the braces. After the definition we can declare variables to be of this ‘new’ type as below.

enum identifier V1, V2, V3, ……… Vn

The enumerated variables V1, V2, ….. Vn can have only one of the values value1, value2 ….. value n

Example:

enum day {Monday, Tuesday, …. Sunday};
enum day week_st, week end;
week_st = Monday;
week_end = Friday;
if(wk_st == Tuesday)
week_en = Saturday;