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Friday, August 8, 2008

C# interview Questions2

C# Interview Questions
General Questions
1. Does C# support multiple-inheritance?
No, use interfaces instead.
2. When you inherit a protected class-level variable, who is it available to?
Classes in the same namespace.
3. Are private class-level variables inherited?
Yes, but they are not accessible. Although they are not visible or accessible via the class interface, they are inherited.
4. Describe the accessibility modifier “protected internal”.
It is available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).
1. To do: Confirm the “within the same assembly” portion.
5. C# provides a default class constructor for me. I decide to write a constructor that takes a string as a parameter, but want to keep the constructor that has no parameter. How many constructors should I write?
Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there’s no implementation in it.
6. What’s the top .NET class that everything is derived from?
System.Object.
7. What does the term immutable mean?
1. answer the question.
8. What’s the difference between System.String and System.StringBuilder classes?
System.String is immutable. System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.
9. What’s the advantage of using System.Text.StringBuilder over System.String?
StringBuilder is more efficient in cases where there is a large amount of string manipulation. Strings are immutable, so each time it’s being operated on, a new instance is created.
10. Can you store multiple data types in System.Array?
No.
11. What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
The first one performs a deep copy of the array, the second one is shallow.
1. To do: improve the answer.
12. How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.
13. What’s the .NET class that allows the retrieval of a data element using a unique key?
HashTable.
14. What class is underneath the SortedList class?
A sorted HashTable.
15. Will the finally block get executed if an exception has not occurred?¬
Yes.
16. What’s the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception?
A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}.
1. To do: Bad question. Re-word.
17. Can multiple catch blocks be executed?
No. Once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block.
18. Explain the three services model commonly know as a three-tier application.
Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
19. What is the role of the DataReader class in ADO.NET connections?
It returns a read-only dataset from the data source when the command is executed.
1. To do: Improve the answer.
Class Questions
20. How do you inherit from a class in C#?
Place a colon and then the name of the base class.
21. Can you prevent your class from being inherited by another class?
Yes. The keyword “sealed” will prevent the class from being inherited.
22. Can you allow a class to be inherited, but prevent the method from being over-ridden?
Yes. Just leave the class public and make the method sealed.
23. What’s an abstract class?
A class that cannot be instantiated. An abstract class is a class that must be inherited and have the methods overridden. An abstract class is essentially a blueprint for a class without any implementation.
24. When do you absolutely have to declare a class as abstract?
1. When at least one of the methods in the class is abstract.
2. When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden.
25. What’s an interface class?
It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.
26. Why can’t you specify the accessibility modifier for methods inside the interface?
They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it’s public by default.
1. To do: Clean up this answer.
27. Can you inherit multiple interfaces?
Yes, why not.
1. To do: Need a better answer.
28. And if they have conflicting method names?
It’s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay.
29. What’s the difference between an interface and abstract class?
In an interface class, all methods must be abstract. In an abstract class some methods can be concrete. In an interface class, no accessibility modifiers are allowed, which is ok in an abstract class.
30. What is the difference between a Struct and a Class?
Structs are value-type variables and are thus saved on the stack -> additional overhead but faster retrieval. Another difference is that structs CANNOT inherit. (questions courtesy of Eyal)
Method and Property Questions
31. What’s the implicit name of the parameter that gets passed into the set method/property of a class?
value. The data type of the value parameter is defined by whatever data type the property is declared as.
32. What does the keyword “virtual” declare for a method or property?
The method or property can be overridden.
33. How is method overriding different from method overloading?
When overriding a method, you change the behavior of the method for the derived class. Overloading a method simply involves having another method with the same name within the class.
34. Can you declare an override method to be static if the original method is non-static?
No. The signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.
1. To do: Re-word the answer for better clarity.
35. Can you override private virtual methods?
No. Private methods are not accessible outside the class.
1. Original answer: No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.
2. To do: Can a private method even be declared a virtual?
36. What are the different ways a method can be overloaded?
Different parameter data types, different number of parameters, different order of parameters.
37. If a base class has a number of overloaded constructors, and an inherited class has a number of overloaded constructors; can you enforce a call from an inherited constructor to a specific base constructor?
Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.
1. To do: question is to complex. It can be stated better.
38. Why is it a bad idea to throw your own exceptions?
Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block?
Throwing your own exceptions signifies some design flaws in the project.
39. What’s a delegate?
A delegate object encapsulates a reference to a method.
40. What’s a multicast delegate?
It’s a delegate that points to and eventually fires off several methods.
1. To do: Need a better answer.
Assembly Questions
41. How is the DLL Hell problem solved in .NET?
Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly.
42. What are the ways to deploy an assembly?
An MSI installer, a CAB archive, and XCOPY command.
43. What is a satellite assembly?
When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies.
44. What namespaces are necessary to create a localized application?
System.Globalization and System.Resources.
XML Documentation Questions
45. What’s the difference between // comments, /* */ comments and /// comments?
Single-line comments, multi-line comments, and XML documentation comments.
46. How do you generate documentation from the C# file commented properly with a command-line compiler?
Compile it with the /doc switch.
47.What is the difference between and XML documentation tag?
Single line code example and multiple-line code example.
1. To do: Bad question
48. Is XML case-sensitive?
Yes.
Debugging and Testing Questions
49. What debugging tools come with the .NET SDK?
1. CorDBG – command-line debugger. To use CorDbg, you must compile the original C# file using the /debug switch.
2. DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR.
50. What does the “This” window show in the debugger?
It points to the object that’s pointed to by this reference. Object’s instance data is shown.
1. To do: Need a better answer.
51. What does assert() method do?
In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true.
52. What’s the difference between the Debug class and Trace class?
Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds.
53. Why are there five tracing levels in System.Diagnostics.TraceSwitcher?
The tracing dumps can be quite verbose. For applications that are constantly running you run the risk of overloading the machine and the hard drive. Five levels range from None to Verbose, allowing you to fine-tune the tracing activities.
54. Where is the output of TextWriterTraceListener redirected?
To the Console or a text file depending on the parameter passed to the constructor.
55. How do you debug an ASP.NET Web application?
Attach the aspnet_wp.exe process to the DbgClr debugger.
56. What are three test cases you should go through in unit testing?
1. Positive test cases (correct data, correct output).
2. Negative test cases (broken or missing data, proper handling).
3. Exception test cases (exceptions are thrown and caught properly).
57. Can you change the value of a variable while debugging a C# application?
Yes. If you are debugging via Visual Studio.NET, just go to Immediate window.
ADO.NET and Database Questions
58. What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET?
SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix. OLE-DB.NET is a .NET layer on top of the OLE layer, so it’s not as fastest and efficient as SqlServer.NET.
59. What is the wildcard character in SQL?
Let’s say you want to query database with LIKE for all employees whose name starts with La. The wildcard character is %, the proper query with LIKE would involve ‘La%’.
60. Explain ACID rule of thumb for transactions.
A transaction must be:
1. Atomic - it is one unit of work and does not dependent on previous and following transactions.
2. Consistent - data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t.
3. Isolated - no transaction sees the intermediate results of the current transaction).
4. Durable - the values persist if the data had been committed even if the system crashes right after.
61. What connections does Microsoft SQL Server support?
Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and password).
62. Which one is trusted and which one is untrusted?
Windows Authentication is trusted because the username and password are checked with the Active Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the transaction.
1. To do: ask the question better.
63. Why would you use untrusted verificaion?
Web Services might use it, as well as non-Windows applications.
1. To do: answer better.
64. What does the Initial Catalog parameter define in the connection string?
The database name to connect to.
65. What is the data provider name to connect to an Access database?
Microsoft.Access.
66. What does the Dispose method do with the connection object?
Deletes it from the memory.
1. To do: answer better. The current answer is not entirely correct.
67. What is a pre-requisite for connection pooling?
Multiple processes must agree that they will share the same connection, where every parameter is the same, including the security settings. The connection string must be identical.
Q1. What is Code Access Security (CAS)?

Code access security is used to ensure that access to protected resources
and operations is allowed only if the security policy allows it.

To use CAS, the code should be verifiably type-safe code - i.e., code that can be verified by the JIT compiler to be type-safe (note that in some cases, the code may be type-safe, but the JIT compiler cannot verify it to be type-safe). Type-safe code accesses only the memory locations it is authorized to access, and only in well-defined, allowable ways.

At runtime, the .NET security system ensures controlled access to protected resources and operations by walking the call stack - each caller in the stack must have the permissions being demanded for the operation being performed. If not, the operation fails and an exception is thrown.

For more on code access security and related topics refer to:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconintroductiontocodeaccesssecurity.asp

Q2. Compare declarative versus imperative security

Declarative security is implemented via attributes. No explicit code is required to implement this.

Imperative security is implemented by explicitly coding the security requirements. An instance of the permission object is created and security calls are issued.

Q3. What is the difference between Demand and Assert?

Demand - calling code can access the resource protected by a permission demand through the code that calls this method, only if callers higher in the stack have been granted permission to access the resource. Results in a stack walk.

Assert - calling code can access the resource protected by a permission demand through the code that calls this method, even if callers higher in the stack have not been granted permission to access the resource. Does not result in a stack walk.

Q4. What is the difference between Demand and LinkDemand.

• Demand specifies that code access security stack walk must occur and all callers on the stack must have the permission or identity to pass. Demand occurs on every call at runtime.
• LinkDemand happens only at just-in-time (JIT) compilation time and checks only the immediate caller. It does not check the caller's caller.

Q5. What is an Application Domain?
An application domain represents isolation/scoping unit for a .NET
application. .NET allows multiple applications to be loaded in a single process. It achieves this by loading each application in its own independent application domain.

Each application domain is isolated from all other application domains. You can think of application domains as lightweight processes with a process. This is more efficient than creating a separate process for each application and provides the same benefit (isolation).

Use System.AppDomain to create application domains programmatically. CLR itself runs in an application domain called the default domain.

Q6. How do you handle errors in VB.NET and C#?

C# and VB.NET use structured error handling (unlike VB6 and earlier versions where error handling was implemented using Goto statement). Error handling in both VB.NET and C# is implemented using Try..Catch..Finally construct (C# uses lower case construct – try...catch...finally).

Q7. What is the purpose of the finally block?

A. The code in finally block is guaranteed to run, irrespective of whether an error occurs or not. Critical portions of code, for example release of file handles or database connections, should be placed in the finally block.
Q1. What is the difference between Reference and Value types?

A variable in .NET can be of Reference type or Value type.

Reference types are allocated on the run-time heap and are accessed through a reference to the memory location where they are stored. Value types are stored on the stack.

Assigning a variable to another reference type variable creates a copy of the reference. Assigning a variable to another value type variable creates a copy of the actual value.

Reference type variables can be null. Value type variables cannot be null.


Q2. Is String a value or reference type? How about integers?

A. String is a reference type. Integer, double, single, etc are value types.


Q3. What do the terms Boxing and UnBoxing mean?

A. Boxing refers to conversion of a value type to a reference type.
Unboxing is the conversion of an object (i.e. reference) to a value type.


Q4. What are Namespaces?

Namespaces allow logical grouping of objects in an assembly. Namespaces also prevent ambiguous references to objects. For example, you can have two classes with the same name in two different namespaces. You can specifiy which class you want to refer to by using namespaces. When you use references that specify the the full name of a class including the namespace, you are using fully qualified names. Example: System.Data.SqlClient.SqlConnection is a full qualified name.

To avoid having to use fully qualified names every time (which can be cumbersome), you can use using statement in C# and Imports statement in VB.NET.

An assembly can contain multiple namespaces.

Namespaces can span assemblies, i.e. you can have two classes belonging to the same namespace in two different assemblies.


Q5. Compare Deterministic vs. non-deterministic finalization.

Deterministic finalization –an object, when released by the calling application, is destroyed immediately (if no other references exist) and the Terminate method runs immediately. This is how classic COM behaves.

Non-deterministic finalization - when an object is released by the calling application, it is marked as being unused (if no other references exist) but not destroyed immediately. It “lives” until GC runs and “collects” the object. It cannot be predicted with certainty when such an object will be GC collected and finalized. .NET uses non-deterministic finalization.


Q6. What is Dispose?

A. Dispose is a method that can be called on objects to release resources held by them immediately. If the resource cleanup code is in the Finalize method, the resources used by that object may be held longer than necessary (see question below for more explanation on this).

By convention, objects should implement the IDisposable interface and the Dispose method. The application using such an object can call the Dispose method when it is done using the object.

Q7. What is the downside of relying on Finalize method to cleanup resources?

A. Finalize method runs when the object is garbage collected. Since .NET does not have deterministic finalization, the exact time at which Finalize method will run is unpredictable. In fact, Finalize method may not run at all – if sufficient memory is available at all times, garbage collection may not occur. As a result, clean up tasks, such as – closing database connections, releasing file handles, etc, which are done in the Finalize method may not be performed.


Q8. Where should you put code for releasing resources held by an object?

A. Use the Dispose method to call up tasks related to resource cleanup. In the Dispose method, you also need to use GC.SuppressFinalize to ensure that these cleanup tasks are not called again in the Finalize method when the object is garbage collected.

Q10. What is a sealed class?

A. It is a class, which cannot be subclassed. It is a good practice to mark your classes as sealed, if you do not intend them to be subclassed.


Q11. How do you prevent a class from being inherited?

A. Mark it as sealed.


Q12. What are strong names and how do you create one?

Strong names guarantee that an assembly’s name is globally unique. You can think of it as similar to GUID (but not same). In other words, a strong name uniquely identifies an assembly. To create a shared assembly (i.e. one deployed in GAC), you need to give it a strong name.

Strong name is comprised of the following: name of the assembly, version information, public key and digital signature. Culture information is also used, if culture is specified.

Creating a strong name using Visual Studio.NET
From the command prompt, create a public/private key pair file using the strong name utility – sn.exe.
In Visual Studio.NET, Specify the location of the key file using the AssemblyKeyFileAttribute.

[assembly:AssemblyKeyFileAttribute("KeyFile.snk")] for C#

[assembly:AssemblyKeyFileAttribute("KeyFile.snk")] for VB.NET

To avoid problems with the path of the key, file you may want to specify the absolute path when specifying the AssemblyKeyFileAttribute.


Q13. What is delay signing and why would you use it?

A. Delay signing is a mechanism to develop strongly named assemblies, without them actually being signed by the developer. The assembly is signed later on by the person having access to the private key. The purpose of delay signing is to secure the private key.


Q14. Explain the terms – assembly and manifest.
An assembly is the smallest unit of deployment and execution in .NET. Usually, there is one file (.exe or .dll) per assembly, although, it is possible to create multi-file assemblies by using allinker.exe.

Manifest refers to the meta-data about an assembly. This meta-data consists information about the assembly version, its methods, properties and events, referenced assemblies, etc. As a result, assemblies are self-describing. Manifest for an assembly is contained in the assembly file itself (.dll or .exe). In case of multi-file assemblies, the manifest for all files is contained only in one file.


Q15. What is Global Assembly Cache (GAC) and how do you deploy an assembly in GAC?

GAC is a repository of shared assemblies (Q16). You can use GACUtil.exe to install an assembly in the GAC.

Q16. What are private and shared assemblies?

Private assemblies are intended to be used by only one application and generally reside in the folder or one of the sub folders of the application using it. Private assemblies need not be strong named (see Q12 for strong name).

Shared assemblies are intended to be used by many applications and are installed in the Global Assembly Cache (GAC). Shared assemblies have to be given a strong name.

1. How big is the datatype int in .NET? 32 bits.
2. How big is the char? 16 bits (Unicode).
3. How do you initiate a string without escaping each backslash? Put an @ sign in front of the double-quoted string.
4. What are valid signatures for the Main function?
• public static void Main()
• public static int Main()
• public static void Main( string[] args )
• public static int Main(string[] args )
5. Does Main() always have to be public? No.
6. How do you initialize a two-dimensional array that you don’t know the dimensions of?
• int [, ] myArray; //declaration
• myArray= new int [5, 8]; //actual initialization
7. What’s the access level of the visibility type internal? Current assembly.
8. What’s the difference between struct and class in C#?
• Structs cannot be inherited.
• Structs are passed by value, not by reference.
• Struct is stored on the stack, not the heap.
9. Explain encapsulation. The implementation is hidden, the interface is exposed.
10. What data type should you use if you want an 8-bit value that’s signed? sbyte.
11. Speaking of Boolean data types, what’s different between C# and C/C++? There’s no conversion between 0 and false, as well as any other number and true, like in C/C++.
12. Where are the value-type variables allocated in the computer RAM? Stack.
13. Where do the reference-type variables go in the RAM? The references go on the stack, while the objects themselves go on the heap. However, in reality things are more elaborate.
14. What is the difference between the value-type variables and reference-type variables in terms of garbage collection? The value-type variables are not garbage-collected, they just fall off the stack when they fall out of scope, the reference-type objects are picked up by GC when their references go null.
15. How do you convert a string into an integer in .NET? Int32.Parse(string), Convert.ToInt32()
16. How do you box a primitive data type variable? Initialize an object with its value, pass an object, cast it to an object
17. Why do you need to box a primitive variable? To pass it by reference or apply a method that an object supports, but primitive doesn’t.
18. What’s the difference between Java and .NET garbage collectors? Sun left the implementation of a specific garbage collector up to the JRE developer, so their performance varies widely, depending on whose JRE you’re using. Microsoft standardized on their garbage collection.
19. How do you enforce garbage collection in .NET? System.GC.Collect();
20. Can you declare a C++ type destructor in C# like ~MyClass()? Yes, but what’s the point, since it will call Finalize(), and Finalize() has no guarantees when the memory will be cleaned up, plus, it introduces additional load on the garbage collector. The only time the finalizer should be implemented, is when you’re dealing with unmanaged code.
21. What’s different about namespace declaration when comparing that to package declaration in Java? No semicolon. Package declarations also have to be the first thing within the file, can’t be nested, and affect all classes within the file.
22. What’s the difference between const and readonly? You can initialize readonly variables to some runtime values. Let’s say your program uses current date and time as one of the values that won’t change. This way you declare
public readonly string DateT = new DateTime().ToString().
23. Can you create enumerated data types in C#? Yes.
24. What’s different about switch statements in C# as compared to C++? No fall-throughs allowed.
25. What happens when you encounter a continue statement inside the for loop? The code for the rest of the loop is ignored, the control is transferred back to the beginning of the loop.
26. Is goto statement supported in C#? How about Java? Gotos are supported in C#to the fullest. In Java goto is a reserved keyword that provides absolutely no functionality.
27. Describe the compilation process for .NET code? Source code is compiled and run in the .NET Framework using a two-stage process. First, source code is compiled to Microsoft intermediate language (MSIL) code using a .NET Framework-compatible compiler, such as that for Visual Basic .NET or Visual C#. Second, MSIL code is compiled to native code.
28. Name any 2 of the 4 .NET authentification methods. ASP.NET, in conjunction with Microsoft Internet Information Services (IIS), can authenticate user credentials such as names and passwords using any of the following authentication methods:
• Windows: Basic, digest, or Integrated Windows Authentication (NTLM or Kerberos).
• Microsoft Passport authentication
• Forms authentication
• Client Certificate authentication
29. How do you turn off SessionState in the web.config file? In the system.web section of web.config, you should locate the httpmodule tag and you simply disable session by doing a remove tag with attribute name set to session.

-- 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).
5. 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) { }
6. 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:
7. using System;
8. public class StringTest
9. {
10. public static void Main(string[] args)
11. {
12. Object nullObj = null; Object realObj = new StringTest();
13. int i = 10;
14. Console.WriteLine("Null Object is [" + nullObj + "]n"
15. + "Real Object is [" + realObj + "]n"
16. + "i is [" + i + "]n");
17. // Show string equality operators
18. string str1 = "foo";
19. string str2 = "bar";
20. string str3 = "bar";
21. Console.WriteLine("{0} == {1} ? {2}", str1, str2, str1 == str2 );
22. Console.WriteLine("{0} == {1} ? {2}", str2, str3, str2 == str3 );
23. }
24. }
Output:
Null Object is []
Real Object is [StringTest]
i is [10]
foo == bar ? False
bar == bar ? True
25. 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:
26. using System;
27. [assembly : MyAttributeClass] class X {}
Note that in an IDE-created project, by convention, these attributes are placed in AssemblyInfo.cs.
28. 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.
29. 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:
30. lock(obj) { // code }
translates to
try {
CriticalSection.Enter(obj);
// code
}
finally
{
CriticalSection.Exit(obj);
}
31. How do you directly call a native function exported from a DLL? - Here’s a quick example of the DllImport attribute in action:
32. using System.Runtime.InteropServices;
33. class C
34. {
35. [DllImport("user32.dll")]
36. public static extern int MessageBoxA(int h, string m, string c, int type);
37. public static int Main()
38. {
39. return MessageBoxA(0, "Hello World!", "Caption", 0);
40. }
41. }
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.
42. 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.
1. Are private class-level variables inherited? - Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.
2. Why does DllImport not work for me? - All methods marked with the DllImport attribute must be marked as public static extern.
3. Why does my Windows application pop up a console window every time I run it? - Make sure that the target type set in the project properties setting is set to Windows Application, and not Console Application. If you’re using the command line, compile with /target:winexe, not /target:exe.
4. Why do I get an error (CS1006) when trying to declare a method without specifying a return type? - If you leave off the return type on a method declaration, the compiler thinks you are trying to declare a constructor. So if you are trying to declare a method that returns nothing, use void. The following is an example: // This results in a CS1006 error public static staticMethod (mainStatic obj) // This will work as wanted public static void staticMethod (mainStatic obj)
5. Why do I get a syntax error when trying to declare a variable called checked? - The word checked is a keyword in C#.
6. Why do I get a security exception when I try to run my C# app? - Some security exceptions are thrown if you are working on a network share. There are some parts of the frameworks that will not run if being run off a share (roaming profile, mapped drives, etc.). To see if this is what’s happening, just move the executable over to your local drive and see if it runs without the exceptions. One of the common exceptions thrown under these conditions is System.Security.SecurityException. To get around this, you can change your security policy for the intranet zone, code group 1.2, (the zone that running off shared folders falls into) by using the caspol.exe tool.
7. Why do I get a CS5001: does not have an entry point defined error when compiling? - The most common problem is that you used a lowercase ‘m’ when defining the Main method. The correct way to implement the entry point is as follows: class test { static void Main(string[] args) {} }
8. What optimizations does the C# compiler perform when you use the /optimize+ compiler option? - The following is a response from a developer on the C# compiler team: We get rid of unused locals (i.e., locals that are never read, even if assigned). We get rid of unreachable code. We get rid of try-catch with an empty try. We get rid of try-finally with an empty try. We get rid of try-finally with an empty finally. We optimize branches over branches: gotoif A, lab1 goto lab2: lab1: turns into: gotoif !A, lab2 lab1: We optimize branches to ret, branches to next instruction, and branches to branches.
9. What is the syntax for calling an overloaded constructor within a constructor (this() and constructorname() does not compile)? - The syntax for calling another constructor is as follows: class B { B(int i) { } } class C : B { C() : base(5) // call base constructor B(5) { } C(int i) : this() // call C() { } public static void Main() {} }
10. What is the equivalent to regsvr32 and regsvr32 /u a file in .NET development? - Try using RegAsm.exe. Search MSDN on Assembly Registration Tool.
11. What is the difference between a struct and a class in C#? - From language spec: The list of similarities between classes and structs is as follows. Longstructs can implement interfaces and can have the same kinds of members as classes. Structs differ from classes in several important ways; however, structs are value types rather than reference types, and inheritance is not supported for structs. Struct values are stored on the stack or in-line. Careful programmers can sometimes enhance performance through judicious use of structs. For example, the use of a struct rather than a class for a Point can make a large difference in the number of memory allocations performed at runtime. The program below creates and initializes an array of 100 points. With Point implemented as a class, 101 separate objects are instantiated-one for the array and one each for the 100 elements.
12. My switch statement works differently than in C++! Why? - C# does not support an explicit fall through for case blocks. The following code is not legal and will not compile in C#:
13. switch(x)
14. {
15. case 0: // do something
16. case 1: // do something as continuation of case 0
17. default: // do something in common with
18. //0, 1 and everything else
19. break;
20. }
To achieve the same effect in C#, the code must be modified as shown below (notice how the control flows are explicit):
class Test
{
public static void Main() {
int x = 3;
switch(x)
{
case 0: // do something
goto case 1;
case 1: // do something in common with 0
goto default;
default: // do something in common with 0, 1, and anything else
break;
}
}
}
21. Is there regular expression (regex) support available to C# developers? - Yes. The .NET class libraries provide support for regular expressions. Look at the System.Text.RegularExpressions namespace.
22. Is there any sample C# code for simple threading? - Yes:
23. using System;
24. using System.Threading;
25. class ThreadTest
26. {
27. public void runme()
28. {
29. Console.WriteLine("Runme Called");
30. }
31. public static void Main(String[] args)
32. {
33. ThreadTest b = new ThreadTest();
34. Thread t = new Thread(new ThreadStart(b.runme));
35. t.Start();
36. }
}
37. Is there an equivalent of exit() for quitting a C# .NET application? - Yes, you can use System.Environment.Exit(int exitCode) to exit the application or Application.Exit() if it’s a Windows Forms app.
38. Is there a way to force garbage collection? - Yes. Set all references to null and then call System.GC.Collect(). If you need to have some objects destructed, and System.GC.Collect() doesn’t seem to be doing it for you, you can force finalizers to be run by setting all the references to the object to null and then calling System.GC.RunFinalizers().
39. Is there a way of specifying which block or loop to break out of when working with nested loops? - The easiest way is to use goto:
40. using System;
41. class BreakExample
42. {
43. public static void Main(String[] args) {
44. for(int i=0; i<3; i++)
45. {
46. Console.WriteLine("Pass {0}: ", i);
47. for( int j=0 ; j<100 ; j++ )
48. {
49. if ( j == 10)
50. goto done;
51. Console.WriteLine("{0} ", j);
52. }
53. Console.WriteLine("This will not print");
54. }
55. done:
56. Console.WriteLine("Loops complete.");
57. }
}
58. Is it possible to restrict the scope of a field/method of a class to the classes in the same namespace? - There is no way to restrict to a namespace. Namespaces are never units of protection. But if you’re using assemblies, you can use the ‘internal’ access modifier to restrict access to only within the assembly.
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.

1. What do you know about .NET assemblies? Assemblies are the smallest units of versioning and deployment in the .NET application. Assemblies are also the building blocks for programs such as Web services, Windows services, serviced components, and .NET remoting applications.
2. What’s the difference between private and shared assembly? Private assembly is used inside an application only and does not have to be identified by a strong name. Shared assembly can be used by multiple applications and has to have a strong name.
3. What’s a strong name? A strong name includes the name of the assembly, version number, culture identity, and a public key token.
4. How can you tell the application to look for assemblies at the locations other than its own install? Use the
directive in the XML .config file for a given application.

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