Page 36 - Programming Microcontrollers in C

Other Types 21

will result in FALSE being 0, TRUE 1, Sun 1, Mon 2, and so
forth to Sat 7. Note that it is not necessary to assign a tag name to
an enum.
An enum is typed at declaration time. Therefore, the values cre­
ated by an enum are indeed numerical values. This differs from the
#define because the statement
#define FALSE 0

will cause the character ‘0’ to be inserted into the source code when­
ever the label FALSE is encountered. As such, the #defineconstruct
is a character substitution technique or a macro expansion. The re­
sult of an enum is a numerical substitution. The #define construct,
being a simple character substitution, has no typing attached to its
arguments. Constants created by an enum are typed, and therefore,
will avoid many of the potential hazards of dealing with untyped
variables.
Let us examine how one might use a type created with an enum
construct. The following enum defines two constants

enum direction {LEFT,RIGHT};
In a program, a definition statement

enum direction d;
will cause a variable d to be created. The acceptable values for d are
the names LEFT and RIGHT. We know, of course, that the numerical
value for LEFT is 0 and the value for RIGHT. Within your program,
you can assign and test the value of d. For example,

if(d==LEFT)
do something

or
if(d==RIGHT)
do something else

or
d = RIGHT;

As stated earlier, the acceptable values for d are LEFT and RIGHT.
There is no checking within the program to see if the programmer