ADD AN INDEXER

An indexer gives your class the ability to behave as an array. If you have a class with many elements, then an indexer lets you sort that information so

your program can get the element it needs from your class.

C# gives you two methods for adding an indexer to a class or an interface. You can add the indexer directly into your program or, if you add a class to your interface, you can add it using the Add C# Interface Indexer Wizard.

Class and interface index accessors come in two forms: get and set. The get accessor returns the type of the indexer.

The set accessor sets the value of the accessor type. The get and set accessors use the same access modifiers as the indexer declaration itself; the access modifiers for get and set must be as accessible as the indexer itself.

You can add an indexer to an interface through the Add C# Interface Indexer Wizard in the Class View window. The Add C# Interface Indexer Wizard contains fields so you can enter the indexer type, the parameter type, the parameter name, and any comments. After you finish entering data into the wizard, C# will create the skeleton of the indexer for you so you can add the indexer accessors.

■ The New Project window

.NET appears.

Á Click the Class View tab.

‡ Click the plus sign () next to the method name.

° Click the plus sign () next to the {} method name.

· Right-click the class name to open the pop-up menu.

‚ Click Add.

— Click Add Indexer.

If you declare more than one indexer in the same class or interface, then the signature for each index must be unique.

TYPE THIS:

using System; class Indexer

{

private int [] Array1 = new int[20]; public int this [int Index]

{

get

{

if (index < 0 | | index >= 20) return 0;

}

set

{

if (!(index < 0 | | index >= 20)) Array1[index] = amount;

}

}

public int [] Array2 = new int[50]; public int this [int Index]

USING ARRAYS 7

RESULT:

You will get an error and your program will not run because you cannot have the same index signature (Index).

■ The C# Indexer Wizard window appears.

± Type the indexer parameter name in the Parameter name field.

¡ Click Add.

■ The parameter appears in the parameter list field.

™ Add an indexer comment in the Comment field.

£ Click Finish.

■ The indexer skeleton code appears in the parent window.

¢ Save the program as the filename.

Enumerations are value types that assign numerical values to elements in an array. By assigning numerical values to elements, enumerations let you acquire those

elements quickly for further processing.

C# assigns the first element in the array the number zero (0) and each successive element in the array receives a successive number. For example, if you enumerate an array with the 12 months of the year, January will receive the number 0 and C# will continue until the end of the array when December gets the number 11.

An enumeration is a special type of array that you declare using the enum keyword. Like an array, you can set

accessibility attributes and access modifiers. The enum elements appear within curly brackets ({}) separated by commas just as array elements do. The key difference between an enumeration and an array is that an enumeration can only be of an integral type, and the default integral type is int. Because enumerations only assign integers to their elements, the only integral type that you cannot include is the char type.

You can change the enumeration value by assigning a number to the first value in the element list, and all successive elements in the list will receive successive numbers. For example, if you give January the number 1, then C# assigns December the number 12.

Properties

› Type a name for the file.

ˇ Click OK.

Á Type the code that establishes the enumeration, sets the value, and outputs the value to the screen.