Tag Archives: c++ interview questions

C# Interview Questions and Answers | C# Interview Sample Questions

  • What’s the advantage of using System.Text.StringBuilder over System.String? StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each time it’s being operated on, a new instance is created.
  • Can you store multiple data types in System.Array? No.
  • 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.
  • How can you sort the elements of the array in descending order? By calling Sort() and then Reverse() methods.
  • What’s the .NET datatype that allows the retrieval of data by a unique key? HashTable.
  • What’s class SortedList underneath? A sorted HashTable.
  • Will finally block get executed if the exception had not occurred? Yes.
  • 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 {}.
  • 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.
  • 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.
  • What’s a delegate? A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.
  • What’s a multicast delegate? It’s a delegate that points to and eventually fires off several methods.
  • How’s 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.
  • What are the ways to deploy an assembly? An MSI installer, a CAB archive, and XCOPY command.
  • What’s 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.
  • What namespaces are necessary to create a localized application? System.Globalization, System.Resources.
  • What’s the difference between // comments, /* */ comments and /// comments? Single-line, multi-line and XML documentation comments.
  • How do you generate documentation from the c# file commented properly with a command-line compiler? Compile it with a /doc switch.
  • What’s the difference between and XML documentation tag? Single line code example and multiple-line code example.
  • Is XML case-sensitive? Yes, so and are different elements.
  • What debugging tools come with the .NET SDK? CorDBG – command-line debugger, and DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR. To use CorDbg, you must compile the original c# file using the /debug switch.
  • 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.
  • What does assert() 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.
  • 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.
  • Why are there five tracing levels in System.Diagnostics.TraceSwitcher? The tracing dumps can be quite verbose and for some applications that are constantly running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities.
  • Where is the output of TextWriterTraceListener redirected? To the Console or a text file depending on the parameter passed to the constructor.
  • How do you debug an ASP.NET Web application? Attach the aspnet_wp.exe process to the DbgClr debugger.
  • What are three test cases you should go through in unit testing? Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper handling), exception test cases (exceptions are thrown and caught properly).
  • 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.
  • Explain the three services model (three-tier application). Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
  • 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, but it’s a .NET layer on top of OLE layer, so not the fastest thing in the world. ODBC.NET is a deprecated layer provided for backward compatibility to ODBC engines.
  • What’s 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.
  • 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%’.
  • Explain ACID rule of thumb for transactions. Transaction must be Atomic (it is one unit of work and does not dependent on previous and following transactions), Consistent (data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t), Isolated (no transaction sees the intermediate results of the current transaction), Durable (the values persist if the data had been committed even if the system crashes right after).
  • What connections does Microsoft SQL Server support? Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).
  • 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.
  • Why would you use untrusted verificaion? Web Services might use it, as well as non-Windows applications.
  • What does the parameter Initial Catalog define inside Connection String? The database name to connect to.
  • What’s the data provider name to connect to Access database? Microsoft.Access.
  • What does Dispose method do with the connection object? Deletes it from the memory.
  • 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.

C# Interview Questions(91-100)

What is the wildcard character in SQL?
Let us 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%.

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.

What does the This window show in the debugger?
It points to the object that is pointed to by this reference. Object’s instance data is shown.

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 is declared in).

What is an interface class?
It is an abstract class with public abstract methods all of which must be implemented in the inherited classes.

What is a multicast delegate?
It is a delegate that points to and eventually fires off several methods.

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

What does assert() 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.

How do I get deterministic finalization in C#?
In a garbage collected environment, it’s impossible to get true determinism. However, a design pattern that we recommend is implementing IDisposable on any class that contains a critical resource. Whenever this class is consumed, it may be placed in a using statement, as shown in the following example:
using(FileStream myFile = File.Open(@”c:temptest.txt”,
FileMode.Open))
{
int fileOffset = 0;
while(fileOffset < myFile.Length)
{
Console.Write((char)myFile.ReadByte());
fileOffset++;
}
}
When myFile leaves the lexical scope of the using, its dispose method will be called.

How can I get around scope problems in a try/catch?
If you try to instantiate the class inside the try, it’ll be out of scope when you try to access it from the catch block. A way to get around this is to do the following: Connection conn = null;
try
{
conn = new Connection();
conn.Open();
}
finally
{
if (conn != null) conn.Close();
}
By setting it to null before the try block, you avoid getting the CS0165 error (Use of possibly unassigned local variable ‘conn’).

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)

C# Interview Questions(81-90)

Can I define a type that is an alias of another type (like typedef in C++)?
Not exactly. You can create an alias within a single file with the “using” directive: using System; using Integer = System.Int32; // alias
But you can’t create a true alias, one that extends beyond the file in which it is declared. Refer to the C# spec for more info on the ‘using’ statement’s scope.

Is it possible to have different access modifiers on the get/set methods of a property?
No. The access modifier on a property applies to both its get and set accessors. What you need to do if you want them to be different is make the property read-only (by only providing a get accessor) and create a private/internal set method that is separate from the property.

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

Does C# support #define for defining global constants?
No. If you want to get something that works like the following C code:
#define A 1
use the following C# code: class MyConstants
{
public const int A = 1;
}
Then you use MyConstants.A where you would otherwise use the A macro.
Using MyConstants.A has the same generated code as using the literal 1.

Does C# support templates?
No. However, there are plans for C# to support a type of template known as a generic. These generic types have similar syntax but are instantiated at run time as opposed to compile time. You can read more about them here.

Does C# support parameterized properties?
No. C# does, however, support the concept of an indexer from language spec. An indexer is a member that enables an object to be indexed in the same way as an array. Whereas properties enable field-like access, indexers enable array-like access. As an example, consider the Stack class presented earlier. The designer of this class may want to expose array-like access so that it is possible to inspect or alter the items on the stack without performing unnecessary Push and Pop operations. That is, Stack is implemented as a linked list, but it also provides the convenience of array access.
Indexer declarations are similar to property declarations, with the main differences being that indexers are nameless (the name used in the declaration is this, since this is being indexed) and that indexers include indexing parameters. The indexing parameters are provided between square brackets.

Does C# support C type macros?
No. C# does not have macros. Keep in mind that what some of the predefined C macros (for example, __LINE__ and __FILE__) give you can also be found in .NET classes like System.Diagnostics (for example, StackTrace and StackFrame), but they’ll only work on debug builds.

Can you store multiple data types in System.Array?
No.

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

Can you declare the override method static while the original method is non-static?
No, you cannot, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override

Does C# support multiple inheritance?
No, use interfaces instead.

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.

C# interview questions and answers(11-20)

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.

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);
}

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.

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.

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.

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.

What’s a strong name?
A strong name includes the name of the assembly, version number, culture identity, and a public key token.

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.
< probing privatePath=c:\mylibs; bin\debug />
should do the trick. Or you can add additional search paths in the Properties box of the deployed application.

How can you debug failed assembly binds?
Use the Assembly Binding Log Viewer (fuslogvw.exe) to find out the paths searched.

Where are shared assemblies stored?
Global assembly cache.

How can you create a strong name for a .NET assembly?
With the help of Strong Name tool (sn.exe).

Where’s global assembly cache located on the system?
Usually C:\winnt\assembly or C:\windows\assembly .

Can you have two files with the same file name in GAC?
Yes, remember that GAC is a very special folder, and while normally you would not be able to place two files with the same name into a Windows folder, GAC differentiates by version number as well, so it’s possible for MyApp.dll and MyApp.dll to co-exist in GAC if the first one is version 1.0.0.0 and the second one is 1.1.0.0.