C# Developers Interview Questions

Started by Kalyan, Jan 10, 2009, 01:14 AM

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Kalyan

C# Developers Interview Questions

   1.  Is it possible to inline assembly or IL in C# code?  - No.

   2. Is it possible to have a static indexer in C#? - No. Static indexers are not allowed in C#.

   3. If I return out of a try/finally in C#, does the code in the finally-clause run? - Yes. The code in the finally always runs. If you return out of the try block, or even if you do a "goto" out of the try, the finally block always runs:

          using System;
             
          class main
          {
             public static void Main()
             {
                try
                {
                   Console.WriteLine(\"In Try block\");
                   return;
                }
                finally
                {
                   Console.WriteLine(\"In Finally block\");
                }
             }
          }

      Both "In Try block" and "In Finally block" will be displayed. Whether the return is in the try block or after the try-finally block, performance is not affected either way. The compiler treats it as if the return were outside the try block anyway. If it's a return without an expression (as it is above), the IL emitted is identical whether the return is inside or outside of the try. If the return has an expression, there's an extra store/load of the value of the expression (since it has to be computed within the try block).

   4. I was trying to use an "out int" parameter in one of my functions. How should I declare the variable that I am passing to it? - You should declare the variable as an int, but when you pass it in you must specify it as 'out', like the following: int i; foo(out i); where foo is declared as follows: [return-type] foo(out int o) { }

   5. How does one compare strings in C#? - In the past, you had to call .ToString() on the strings when using the == or != operators to compare the strings' values. That will still work, but the C# compiler now automatically compares the values instead of the references when the == or != operators are used on string types. If you actually do want to compare references, it can be done as follows: if ((object) str1 == (object) str2) { ... } Here's an example showing how string compares work:

      using System;
      public class StringTest
      {
         public static void Main(string[] args)
         {
            Object nullObj = null; Object realObj = new StringTest();
            int i = 10;
            Console.WriteLine(\"Null Object is [\" + nullObj + \"]\n\"
               + \"Real Object is [\" + realObj + \"]\n\"
               + \"i is [\" + i + \"]\n\");
               // Show string equality operators
            string str1 = \"foo\";
            string str2 = \"bar\";
            string str3 = \"bar\";
            Console.WriteLine(\"{0} == {1} ? {2}\", str1, str2, str1 == str2 );
            Console.WriteLine(\"{0} == {1} ? {2}\", str2, str3, str2 == str3 );
         }
      }

      Output:

      Null Object is []
      Real Object is [StringTest]
      i is [10]
      foo == bar ? False
      bar == bar ? True

   6. How do you specify a custom attribute for the entire assembly (rather than for a class)? - Global attributes must appear after any top-level using clauses and before the first type or namespace declarations. An example of this is as follows:

      using System;
      [assembly : MyAttributeClass] class X {}

      Note that in an IDE-created project, by convention, these attributes are placed in AssemblyInfo.cs.
   7. How do you mark a method obsolete? -

      [Obsolete] public int Foo() {...}

      or

      [Obsolete(\"This is a message describing why this method is obsolete\")] public int Foo() {...}

      Note: The O in Obsolete is always capitalized.
   8. How do you implement thread synchronization (Object.Wait, Notify,and CriticalSection) in C#? - You want the lock statement, which is the same as Monitor Enter/Exit:

      lock(obj) { // code }

      translates to

      try {
         CriticalSection.Enter(obj);
         // code
      }
      finally
      {
         CriticalSection.Exit(obj);
      }

   9. How do you directly call a native function exported from a DLL? - Here's a quick example of the DllImport attribute in action:

      using System.Runtime.InteropServices; \
      class C
      {
         [DllImport(\"user32.dll\")]
         public static extern int MessageBoxA(int h, string m, string c, int type);
         public static int Main()
         {
            return MessageBoxA(0, \"Hello World!\", \"Caption\", 0);
         }
      }

      This example shows the minimum requirements for declaring a C# method that is implemented in a native DLL. The method C.MessageBoxA() is declared with the static and external modifiers, and has the DllImport attribute, which tells the compiler that the implementation comes from the user32.dll, using the default name of MessageBoxA. For more information, look at the Platform Invoke tutorial in the documentation.

  10. How do I simulate optional parameters to COM calls? - You must use the Missing class and pass Missing.Value (in System.Reflection) for any values that have optional parameters.

Kalyan

C# Developers Interview Questions

A representative of a high-tech company in United Kingdom sent this in today noting that the list was used for interviewing a C# .NET developer. Any corrections and suggestions would be forwarded to the author. I won't disclose the name of the company, since as far as I know they might still be using this test for prospective employees. Correct answers are in green color.

1) The C# keyword .int. maps to which .NET type?

   1.

      System.Int16
   2.

      System.Int32
   3.

      System.Int64
   4.

      System.Int128

2) Which of these string definitions will prevent escaping on backslashes in C#?

   1.

      string s = #.n Test string.;
   2.

      string s = ..n Test string.;
   3.

      string s = @.n Test string.;
   4.

      string s = .n Test string.;

3) Which of these statements correctly declares a two-dimensional array in C#?

   1.

      int[,] myArray;
   2.

      int[][] myArray;
   3.

      int[2] myArray;
   4.

      System.Array[2] myArray;

4) If a method is marked as protected internal who can access it?

   1.

      Classes that are both in the same assembly and derived from the declaring class.
   2.

      Only methods that are in the same class as the method in question.
   3.

      Internal methods can be only be called using reflection.
   4.

      Classes within the same assembly, and classes derived from the declaring class.

5) What is boxing?

    a) Encapsulating an object in a value type.

    b) Encapsulating a copy of an object in a value type.

    c) Encapsulating a value type in an object.

    d) Encapsulating a copy of a value type in an object.

6) What compiler switch creates an xml file from the xml comments in the files in an assembly?

   1.

      /text
   2.

      /doc
   3.

      /xml
   4.

      /help

7) What is a satellite Assembly?

   1.

      A peripheral assembly designed to monitor permissions requests from an application.
   2.

      Any DLL file used by an EXE file.
   3.

      An assembly containing localized resources for another assembly.
   4.

      An assembly designed to alter the appearance or .skin. of an application.

8) What is a delegate?

   1.

      A strongly typed function pointer.
   2.

      A light weight thread or process that can call a single method.
   3.

      A reference to an object in a different process.
   4.

      An inter-process message channel.

9) How does assembly versioning in .NET prevent DLL Hell?

   1.

      The runtime checks to see that only one version of an assembly is on the machine at any one time.
   2.

      .NET allows assemblies to specify the name AND the version of any assemblies they need to run.
   3.

      The compiler offers compile time checking for backward compatibility.
   4.

      It doesn.t.

10) Which .Gang of Four. design pattern is shown below?

    public class A {

        private A instance;

        private A() {

        }

        public
    static A Instance {

            get

            {

                if ( A == null )

                    A = new A();

                return instance;

            }

        }

    }

   1.

      Factory
   2.

      Abstract Factory
   3.

      Singleton
   4.

      Builder

11) In the NUnit test framework, which attribute must adorn a test class in order for it to be picked up by the NUnit GUI?

   1.

      TestAttribute
   2.

      TestClassAttribute
   3.

      TestFixtureAttribute
   4.

      NUnitTestClassAttribute

12) Which of the following operations can you NOT perform on an ADO.NET DataSet?

   1.

      A DataSet can be synchronised with the database.
   2.

      A DataSet can be synchronised with a RecordSet.
   3.

      A DataSet can be converted to XML.
   4.

      You can infer the schema from a DataSet.

13) In Object Oriented Programming, how would you describe encapsulation?

   1.

      The conversion of one type of object to another.
   2.

      The runtime resolution of method calls.
   3.

      The exposition of data.
   4.

      The separation of interface and implementation.

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