Programming in C

324 Chapter 14 More on Data Types

Program 14.1 Output

Enter month number: 5

Number of days is 31

Program 14.1 Output (Rerun)

Enter month number: 2

Number of days is 28

...or 29 if it’s a leap year

Enumeration identifiers can share the same value. For example, in

enum switch { no=0, off=0, yes=1, on=1 };

assigning either the value noor offto an enum switchvariable assigns it the value 0 ;

assigning either yesor onassigns it the value 1.

Explicitly assigning an integer value to an enumerated data type variable can be done

with the type cast operator. So if monthValueis an integer variable that has the value 6 ,

for example, the expression

thisMonth = (enum month) (monthValue - 1);

is permissible and assigns the value 5 to thisMonth.

When writing programs with enumerated data types, try not to rely on the fact that

the enumerated values are treated as integers. Instead, try to treat them as distinct data

types.The enumerated data type gives you a way to associate a symbolic name with an

integer number. If you subsequently need to change the value of that number, you must

change it only in the place where the enumeration is defined. If you make assumptions

based on the actual value of the enumerated data type, you defeat this benefit of using an

enumeration.

The variations permitted when defining an enumerated data type are similar to those

permitted with structure definitions:The name of the data type can be omitted, and

variables can be declared to be of the particular enumerated data type when the type is

defined. As an example showing both of these options, the statement

enum { east, west, south, north } direction;

defines an (unnamed) enumerated data type with values east,west,south, or north,

and declares a variable directionto be of that type.

Enumerated type definitions behave like structure and variable definitions as far as

their scope is concerned: Defining an enumerated data type within a block limits the

scope of that definition to the block. On the other hand, defining an enumerated data

type at the beginning of the program, outside of any function, makes the definition

global to the file.

When defining an enumerated data type, you must make certain that the enumeration

identifiers are unique with respect to other variable names and enumeration identifiers

defined within the same scope.