1. 只有C#内置类型（int,double,long等）可以声明为const;结果、类和数组不能声明为const。
2. readonly 是在字段上使用的修饰符，直接以类名.字段访问。
3. const 必须在申明中初始化。之后不能再修改。
4. readonly可以在申明中初始化，也可以在构造函数中初始化，其它情况不能修改。
namespace const_and_readonly
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Half a year have {0} Moths", Calendar.Moths/2); //直接类名.字段访问const字段
Calendar test1 = new Calendar();
Console.WriteLine("Every year has {0} weeks and {1} days", test1._weeks, test1._days);//readonly字段通过实例访问
Calendar test2 = new Calendar(31, 4);
Console.WriteLine("January has {0} weeks and {1} days", test2._weeks ,test2 ._days);
Console.ReadKey();
}
}
class Calendar
{
public const int Moths = 12; //const必须在声明中初始化
public readonly int _days=365; //readonly在声明中初始化
public readonly int _weeks;
public Calendar() //readonly在构造函数内初始化
{
_weeks = 52;
}
public Calendar(int days,int weeks) //readonly在构造函数内初始化
{
_days = days;
_weeks = weeks;
}
public void setvalue(int days,int weeks)
{
// _days = days; 无法对只读字段赋值
//_weeks = weeks; 无法对只读字段赋值
} }