圆类c#编程

class Circle
{
private const float PI = 3.14159F;
private float r;

public float R
{
get { return r; }
set
{
if (value >= 0)
r = value;
else
r = 0;
}
}
public Circle()
{
r = 0;
}
public Circle(float r)
{
this.r = r;
}
/// <summary>
/// 计算圆的面积
/// </summary>
/// <returns></returns>
public float AreaOfCircle()
{
return PI * R * R;
}
/// <summary>
/// 计算圆的周长
/// </summary>
/// <returns></returns>
public float LengthOfCir