unsafe -- C# Keyword

unsafe -- C# Keyword
           The unsafe keyword denotes an unsafe context, which is required for any operation involving pointers.

Without  Parameter

unsafe
{
    // Unsafe context: can use pointers here.
}

With Parameter(s)

unsafe static void <Method Name>(<data Type> <var name>)
{
    // Unsafe context: can use pointers here.
}

static -- C# Keyword

static  -- C# Keyword

• Use the static modifier to declare a static member, which belongs to the type itself rather than to a specific object.
•  The static modifier can be used with classes, fields, methods, properties, operators, events, and constructors, but it cannot be used with indexers, destructors, or types other than classes.

static class <Class Name>
    {
        public static void <Method Name>() { /*...*/ }
        public static void <Method Name>() { /*...*/  }
    }

sealed -- C# Keyword

sealed  -- C# Keyword

•  When applied to a class, the sealed modifier prevents other classes from inheriting from it.
•   In the following example, class B inherits from class A, but no class can inherit from class B.

class A {}  
sealed class B : A {}

readonly -- C# Keyword

readonly -- C# Keyword

•  The readonly keyword is a modifier that you can use on fields.
•   When a field declaration includes a readonly modifier, assignments to the fields introduced by the declaration can only occur as part of the declaration or in a constructor in the same class.

readonly <data Type> <var Name>;

override -- C# Keyword

override -- C# Keyword

•  The override modifier is required to extend or modify the abstract or virtual implementation of an inherited method, property, indexer, or event.
• An override declaration cannot change the accessibility of the virtual method.
• Both the override method and the virtual method must have the same access level modifier.
• You cannot use the new, static, or virtual modifiers to modify an override method.

out -- C# Keyword

out -- C# Keyword

• This keyword implemented from VS 2010
•  The out keyword specifies that the type parameter is covariant.
• You can use the out keyword in generic interfaces and delegates.

interface <interface Name><out R> { }

extern -- C# Keyword

extern -- C# Keyword

•  The extern modifier is used to declare a method that is implemented externally.
• A common use of the extern modifier is with the DllImport attribute when you are using Interop services to call into unmanaged code.
• In this case, the method must also be declared as static, 

[DllImport("<dll Name>.dll")]
private static extern void <dll Method Name>();

const -- C# Keyword

const  -- C# Keyword

• You use the const keyword to declare a constant field or a constant local.
•  Constant fields and locals aren't variables and may not be modified.
•  Constants can be numbers, Boolean values, strings, or a null reference.

const <Data Type> <Var Name> = <Set Value>;

Protected -- C# Keyword

Protected  -- C# Keyword:

• The protected keyword is a member access modifier.
• A protected member is accessible within its class and by derived class instances.

 protected <Data Type> <Variable Name>;

async -- C# Keyword

async  -- C# Keyword

• This Keyword is implemented from VS 2012.
•         Use the async modifier to specify that a method, lambda expression, or anonymous method is asynchronous.
•         If you use this modifier on a method or expression, it's referred to as an async method.

public async Task<int> ExampleMethodAsync()
{
    // . . . .

}