C# Interview Questions and Answers (958) - Page 40

Custom types are the complex types which are built by primitive types.
These are created by using class, struct, enum and interface.
Microsoft provided so many custom types to .NET framework that are being used in our own applications.

Fixed is the one of uncommon keyword in C#. The keyword Fixed which can only be used in Unsafe C# code blocks.
Fixed statement sets the pointer to be in a fixed memory address so that,it will not be moved to anywhere even if Garbage Collection Thread is invoked.We have to use Fixed keyword.

For Example:-

fixed (char* pointer = 1)

{

  //Our code

}

Default Keyword returns the default value when the object is not initialized. For example,we all know integers are initialized to 0 if not given any value. Characters are Empty when not given any value,objects are null when not assigned any value.
For Example:-

int x = default(int);//will be assigned to 0.

in is a reserved keyword of C# programming language. in is widely used with foreach loop.

Example,

foreach (char ch in "Hello")

{

    Console.WriteLine(ch); // prints all characters

}

in keyword is also used for some query expressions. Ex: LINQ.

extern is a c# keyword or modifier which calls an external method.
It is mostly used for interop services with DLLImport attribute. This will calls an external method from the particular dll library.
Example,

[DllImport("User32.dll", CharSet = CharSet.Unicode)]

public static extern int MessageBox(IntPtr i, string s1, string s2, int type);



static int Main()

{

    string Name;

    Console.WriteLine("Please type your message here: ");

    Name = Console.ReadLine();

    return MessageBox((IntPtr)0, Name, "Message Box", 0);

}

async is a C# modifier (keyword) used to specify any asynchronous methods. async and await cannot be used with the Main method. async can only return Void or Task. async method can also be run as synchronous if it doesn't include await.

Example,

static async Task<int> FuncAsync()

{

    ..........;

    ......;

}

It compiles the source code into an assembly. It is named as csc.exe.
We can call the C# compiler manually or by using Visual Studio's IDE (Integrated Development Environment).

To compile manually,
1. We have to save our program with extension of '.cs'

2. And then open the command prompt and invoke the compiler like
RootFolder(Windows Directory)\Microsoft .NET\Framework\
i.e, csc MyProgram.cs. It will generate MyProgram.exe.

3. Now to create a library, do like below,
csc /target:library MyProgram.cs.

NOTE: This is objective type question, Please click question title for correct answer.