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<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> return x*x;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> public static double GetPi()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> return 3.14159;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt; LINE-HEIGHT: 13pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">运行</span><span lang="EN-US">mathTest</span><span style="FONT-FAMILY: 宋体">示例，会得到如下结果：</span></p>
<p class="a6" style="MARGIN: 8.15pt 0cm 8.15pt 9.95pt; TEXT-INDENT: 9.95pt"><strong><span lang="EN-US">csc MathTest.cs</span></strong></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Microsoft (R) Visual C# .NET Compiler version 7.10.3052.4</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">for Microsoft (R) .NET Framework version 1.1.4322</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Copyright (C) Microsoft Corporation 2001-2002. All rights reserved.</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">MathTest</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Pi is 3.14159</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Square of 5 is 25</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Value field of math variable contains 30</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Square of 30 is 900</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">从代码中可以看出，</span><span lang="EN-US">MathTest</span><span style="FONT-FAMILY: 宋体">类包含一个字段和一个方法，该字段包含一个数字，该方法计算数字的平方。这个类还包含两个静态方法，返回</span><span lang="EN-US">pi</span><span style="FONT-FAMILY: 宋体">的值，并把数字的平方作为参数传入。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">这个类有一些功能并不是</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">程序设计的好例子。例如，</span><span lang="EN-US">GetPi()</span><span style="FONT-FAMILY: 宋体">通常作为</span><span lang="EN-US">const</span><span style="FONT-FAMILY: 宋体">字段来执行，而好的设计应使用目前还没有介绍的概念。</span></p>
<p class="MsoNormal"><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">Java</span><span style="FONT-FAMILY: 宋体">开发人员应很熟悉这个语法的大多数内容。如果您有</span><span lang="EN-US">VB</span><span style="FONT-FAMILY: 宋体">的编程经验，就会仅把</span><span lang="EN-US">MathTest</span><span style="FONT-FAMILY: 宋体">类看作一个执行字段和方法的</span><span lang="EN-US">VB</span><span style="FONT-FAMILY: 宋体">类模块。</span></p>
<p class="a3" style="MARGIN-TOP: 8.15pt; TEXT-INDENT: 21.45pt"><span lang="EN-US">(3) </span><span style="FONT-FAMILY: 黑体">给方法传递参数</span></p>
<p class="MsoNormal"><span><span style="FONT-FAMILY: 宋体">参数可以通过引用或值传递给方法。在变量通过引用传递给方法时，被调用的方法得到的就是这个变量，所以在方法内部对变量进行的任何改变在方法退出后仍旧发挥作用。而如果变量是通过值传送给方法的，被调用的方法得到的是变量的初始副本，也就是说，在方法退出后，对变量进行的修改会丢失。对于复杂的数据类型，按引用传递的效率更高，因为在按值传递时，必须复制大量的数据。</span></span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">在</span><span lang="EN-US">C#</span><span style="FONT-FAMILY: 宋体">中，所有的参数都是通过值来传递的，除非特别说明。这与</span><span lang="EN-US">C++</span><span style="FONT-FAMILY: 宋体">是相同的，但与</span><span lang="EN-US">VB</span><span style="FONT-FAMILY: 宋体">不同。但是，在理解引用类型的传递过程时需要注意。因为引用类型的对象只包含对象的引用，它们只给方法传递这个引用，而不是对象本身，所以对底层对象的修改会保留下来。相反，值类型的对象包含的是实际数据，所以传递给方法的是数据本身的副本。例如，</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">通过值传递给方法，方法对该</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">的值所作的任何改变都没有改变原</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">对象的值。但如果数组或其他引用类型</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">如类</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">传递给方法后，方法会使用该引用改变这个数组中的值，而新值会反射到原来的数组对象上。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">下面的例子</span><span lang="EN-US">ParameterTest.cs</span><span style="FONT-FAMILY: 宋体">说明了这一点：</span></p>
<p class="2" style="MARGIN: 8.15pt 0cm 0pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">using System;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">namespace Wrox.ProCSharp. ParameterTestSample</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> class ParameterTest</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> static void SomeFunction(int[] ints, int i)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> ints[0] = 100;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> i = 100;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> public static int Main()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> int i = 0;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> int[] ints = { 0, 1, 2, 4, 8 };</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> // Display the original values</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("i = " + i);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("ints[0] = " + ints[0]);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("Calling SomeFunction...");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> // After this method returns, ints will be changed,</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> // but i will not</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> SomeFunction(ints, i);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("i = " + i);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> Console.WriteLine("ints[0] = " + ints[0]);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> return 0;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="a6" style="MARGIN: 0cm 0cm 8.15pt 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">结果如下：</span></p>
<p class="a6" style="MARGIN: 8.15pt 0cm 8.15pt 9.95pt; TEXT-INDENT: 9.95pt"><strong><span lang="EN-US">csc ParameterTest.cs</span></strong></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Microsoft (R) Visual C# .NET Compiler version 7.10.3052.4</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">for Microsoft (R) .NET Framework version 1.1.4322</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">Copyright (C) Microsoft Corporation 2001-2002. All rights reserved.</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US"> </span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">ParameterTest</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">i = 0</span></p>
<p class="a6" style="BACKGROUND: #f2f2f2; MARGIN-LEFT: 21.45pt; TEXT-INDENT: 18.45pt"><span lang="EN-US">ints[0] = 0</span></p>
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