Const ,Readonly, Static .....Have a Loo0ook

const Keyword

• A constant member is defined at compile time and cannot be changed at runtime.
• Constants are declared as a field, using the const keyword and must be initialized as they are declared.
• Since classes or structures are initialized at run time with the new keyword, and not at compile time, you can't set a constant to a class or structure.
• for example       public const double PI=3.14 
• so we the value of PI will be constant through all the application and can't change it and if we try to change it, will give us compilation error 

readonly Keyword 

• A read only member is like a constant in that it represents an unchanging value
• The difference is that a readonly member can be initialized at runtime, in a constructor as well being able to be initialized as they are declared.
• Because a readonly field can be initialized either at the declaration or in a constructor
• readonly fields can have different values depending on the constructor used
• A readonly member can hold a complex object by using the new keyword at initialization.
• readonly members cannot hold enumerations.
• readonly members are not implicitly static, and therefore the static keyword can be applied to a readonly field explicitly if required.

static Keyword 

• Use of the static modifier to declare a static member, means that the member is no longer tied to a specific object.
• This means that the member can be accessed without creating an instance of the class
• static methods and properties can only access static fields and static events
• The static modifier can be used with classes, fields, methods, properties, operators, events and constructors, but cannot be used with indexers, destructors, or types other than classes.
• To access a static class member, use the name of the class instead of a variable name to specify the location of the member.