今天我们来讲一个用C#如何来描述一个矩形的实例：

    private float length=1.0f;
    private float width=1.0f;

这里声明两个变量，用于代表其长和宽

public float SetLength(float length)
    {
        this.length=length;
        if((length<0.0f)||(length>2.0f))
        {
            Console.WriteLine ("长的取值范围应在1.0-2.0    之内，请重新设值。");
            return 0.0f;
        }
        return width;
    }

这个函数用于定义其长度

  public float SetWidth(float width)
    {
        this.width=width;
        if((width<0.0f)||(width>2.0f))
        {
            Console.WriteLine ("宽的取值范围应在1.0-2.0    之内，请重新设值。"); 
            return 0.0f;
        }
        return width;
    }

该函数用于定义其宽度

    public float GetLength(float length)
    {
        return length;
    }
    public float GetWidth(float width)
    {
        return width;  
    }

这两个函数用于获取其长和宽

public float perimeter()
        {
        return length*2+width*2;
    }
    public float area()
    {
       return length*width;
    }

用于反回其周长和面积 测试类如下

class Rectangle_Test
{
    public static void Main()
    {
        Rectangle r1=new Rectangle ();
        r1.SetLength (1.8f);
        r1.SetWidth (1.2f);
        Console.WriteLine (r1.perimeter ());
        Console.WriteLine (r1.area ());

    }

}
 using System;
class Rectangle
{
    private float length=1.0f;
    private float width=1.0f;

    public float SetLength(float length)
    {
        this.length=length;
        if((length<0.0f)||(length>2.0f))
        {
            Console.WriteLine ("长的取值范围应在1.0-2.0    之内，请重新设值。");
            return 0.0f;
        }
        return width;
    }
    public float SetWidth(float width)
    {
        this.width=width;
        if((width<0.0f)||(width>2.0f))
        {
            Console.WriteLine ("宽的取值范围应在1.0-2.0    之内，请重新设值。"); 
            return 0.0f;
        }
        return width;
    }
    public float GetLength(float length)
    {
        return length;
    }
    public float GetWidth(float width)
    {
        return width;  
    }
    public float perimeter()
        {
        return length*2+width*2;
    }
    public float area()
    {
       return length*width;
    }

}
class Rectangle_Test
{
    public static void Main()
    {
        Rectangle r1=new Rectangle ();
        r1.SetLength (1.8f);
        r1.SetWidth (1.2f);
        Console.WriteLine (r1.perimeter ());
        Console.WriteLine (r1.area ());

    }

}