C# 0 The Complete Reference

PART II

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653

    else

      Console.WriteLine("nums contains no negative values.");

  }

}

The output is shown here:

Contents of nums: 1 4 -1 5 -9

nums contains a negative value.

First negative value is : -1

In the program, the method passed to 

Exists( )

 and 

Find( )

 for the predicate is 

IsNeg( )

.

Notice that 

IsNeg( )

 is declared like this:

static bool IsNeg(int v) {

The methods 

Exists( )

 and 

Find( )

 will automatically pass the elements of the array (in 

sequence) to 

v

. Thus, each time 

IsNeg( )

 is called, 

v

 will contain the next element in the array.

Using an Action

The

Action

 delegate is used by 

Array.ForEach( )

 to perform an action on each element of an 

array. There are various forms of 

Action

, each taking a different number of type parameters. 

The one used here is

public delegate void Action (T 

obj

)

The object to be acted upon is passed in 

obj

. When used with 

ForEach( )

, each element of the 

array is passed to 

obj

 in turn. Thus, through the use of 

ForEach( )

 and 

Action

, you can, in a 

single statement, perform an operation over an entire array.

The following program demonstrates both 

ForEach( )

 and 

Action

. It first creates an 

array of 

MyClass

 objects, then uses the method 

Show( )

 to display the values. Next, it uses 

Neg( )

 to negate the values. Finally, it uses 

Show( )

 again to display the negated values. 

These operations all occur through calls to 

ForEach( )

.

// Demonstrate an Action.

using System;

class MyClass {

  public int i;

  public MyClass(int x) { i = x; }

}

class ActionDemo {

  // An Action method.

  // It displays the value it is passed.

  static void Show(MyClass o) {

    Console.Write(o.i + " ");

  }

  // Another Action method.

  // It negates the value it is passed.

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  static void Neg(MyClass o) {

    o.i = -o.i;

  }

  static void Main() {

    MyClass[] nums = new MyClass[5];

    nums[0] = new MyClass(5);

    nums[1] = new MyClass(2);

    nums[2] = new MyClass(3);

    nums[3] = new MyClass(4);

    nums[4] = new MyClass(1);

    Console.Write("Contents of nums: ");

    // Use action to show the values.

    Array.ForEach(nums, ActionDemo.Show);

    Console.WriteLine();

    // Use action to negate the values.

    Array.ForEach(nums, ActionDemo.Neg);

    Console.Write("Contents of nums negated: ");

    // Use action to show the values again.

    Array.ForEach(nums, ActionDemo.Show);

    Console.WriteLine();

  }

}

The output is shown here:

Contents of nums: 5 2 3 4 1

Contents of nums negated: -5 -2 -3 -4 -1

BitConverter

In programming one often needs to convert a built-in data type into an array of bytes. For 

example, some hardware device might require an integer value, but that value must be sent 

one byte at a time. The reverse situation also frequently occurs. Sometimes data will be 

received as an ordered sequence of bytes that needs to be converted into one of the built-in 

types. For example, a device might output integers, sent as a stream of bytes. Whatever 

your conversion needs, .NET provides the 

BitConverter

 class to meet them.

BitConverter

 is 

static

class. It contains the methods shown in Table 21-13. It defines the 

following field:

public static readonly bool IsLittleEndian

This field is 

true

 if the current environment stores a word with the least significant byte first 

and the most significant byte last. This is called “little-endian” format. 

IsLittleEndian

 is 

false

 if the current environment stores a word with the most significant byte first and the 

least significant byte last. This is called “big-endian” format. Intel Pentium–based machines 

use little-endian format.

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