求方形、圆形、三角形面积周长的C#程序

用接口的方式实现继承多态，可以求方形、圆形和三角形的面积，并且有兴趣的同学可以根据此程序改成抽象类也可以实现功能。

 属性            大小     日期    时间   名称
----------- ---------  ---------- -----  ----

     文件       5632  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\bin\Debug\ConsoleApplication1.exe

     文件      15872  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\bin\Debug\ConsoleApplication1.pdb

     文件      14328  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\bin\Debug\ConsoleApplication1.vshost.exe

     文件        490  2007-07-21 01:33  ConsoleApplication1\ConsoleApplication1\bin\Debug\ConsoleApplication1.vshost.exe.manifest

     文件       2511  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\ConsoleApplication1.csproj

     文件        397  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\obj\Debug\ConsoleApplication1.csproj.FileListAbsolute.txt

     文件       5632  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\obj\Debug\ConsoleApplication1.exe

     文件      15872  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\obj\Debug\ConsoleApplication1.pdb

     文件       2339  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\Program.cs

     文件       1394  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\Properties\AssemblyInfo.cs

     文件        947  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1.sln

    ..A..H.     10752  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1.suo

     目录          0  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\obj\Debug\TempPE

     目录          0  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\bin\Debug

     目录          0  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\obj\Debug

     目录          0  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\bin

     目录          0  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\obj

     目录          0  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1\Properties

     目录          0  2010-08-08 08:42  ConsoleApplication1\ConsoleApplication1

     目录          0  2010-08-08 08:42  ConsoleApplication1

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