User Define Types

Enumerator

To help make programs more readable, the C language allows users to define their own types. Two forms are provided:

enum

This is really just an integer declaration with symbolic names for the values variables of this type can take. Essentially, an enum takes the place of an integer declaration and a set of macros.

For example, instead of using the macros defined in tfdef.h, we can declare an "enumerated type" as:

     enum boolean {FALSE,TRUE};

This defines a type enum boolean (really an integer) that can take on the values FALSE (really 0) or TRUE (really 1). We can then declare a variable of this type:

     enum boolean flag;

and can then write statements like:

     flag = TRUE;

     if(flag == FALSE)

The general form to declare an enumerated type is:

     enum [<tag>] {<identifier> [,<identifier>...} [<variable_name>];

The <tag> is an optional name for the type, and the <identifier>'s are the symbolic names for the values we can assign to a variable of this type. They correspond to integer values starting with 0, from left to right. The optional <variable_name> allows us to declare a variable of this type at the same time we declare the type.

When we declare an enum type, we can also specify the starting integer value for the symbolic names:

     enum days {SUN=1,MON,TUE,WED,THU,FRI,SAT};

     enum days today, tomorrow;

     today = MON;

     tomorrow = today + 1;

     if(tomorrow == SAT) play();

typedef

We can also give our own names to any existing type using typedef. The general form is:

     typedef <existing type name> <new type name>;

For example:

     typedef float coefficient;

     typedef int solution;

     solution s1, s2, s3; //these variables are ints

     coefficient c1, c2, c3;// These variables are floats