C# interview questions and answers
1. 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.
2. Can you store multiple data types in System.Array?
No.
3. 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.
4. How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.
5. What’s the .NET datatype that allows the retrieval of data by a unique key? HashTable.
6. What’s class SortedList underneath?
A sorted HashTable.
7. Will finally block get executed if the exception had not occurred?
Yes.
8. 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 {}.
9. 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.
10. 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.
11. What’s a delegate? A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.
12. What’s a multicast delegate? It’s a delegate that points to and eventually fires off several methods.
13. 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.
14. What are the ways to deploy an assembly? An MSI installer, a CAB archive, and XCOPY command.
15. 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.
16. What namespaces are necessary to create a localized application? System.Globalization, System.Resources.
17. What’s the difference between // comments, /* */ comments and /// comments? Single-line, multi-line and XML documentation comments.
18. How do you generate documentation from the C# file commented properly with a command-line compiler? Compile it with a /doc switch.
19. What’s the difference between c and code XML documentation tag?
Single line code example and multiple-line code example.
20. Is XML case-sensitive?
Yes, so and are different elements.
21. 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.
22. 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.
23. 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.
24. 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.
25. 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.
26. Where is the output of TextWriterTraceListener redirected? To the Console or a text file depending on the parameter passed to the constructor.
27. How do you debug an ASP.NET Web application? Attach the aspnet_wp.exe process to the DbgClr debugger.
28. 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).
29. 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.
30. Explain the three services model (three-tier application). Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
31. 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.
32. 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.
33. 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%’.
34. 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).
35. What connections does Microsoft SQL Server support? Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).
36. 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.
37. Why would you use untrusted verificaion? Web Services might use it, as well as non-Windows applications.
38. What does the parameter Initial Catalog define inside Connection String? The database name to connect to.
39. What’s the data provider name to connect to Access database? Microsoft.Access.
40. What does Dispose method do with the connection object? Deletes it from the memory.
41. 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.
42.
A Hashtable object consists of buckets that contain the elements of the collection. A bucket is a virtual subgroup of elements within the Hashtable, which makes searching and retrieving easier and faster than in most collections. Each bucket is associated with a hash code, generated using a hash function and based on the key of the element.
The Dictionary class has the same functionality as the Hashtable class. A Dictionary of a specific type (other than Object) has better performance than a Hashtable for value types because the elements of Hashtable are of type Object and, therefore, boxing and unboxing typically occur if storing or retrieving a value type.
43.What is DLL Hell and how it is solved in .NET?
List
IEnumerable
List
List
a.
It works/executes fast as it is in precompiled mode.
1. 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.
2. Can you store multiple data types in System.Array?
No.
3. 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.
4. How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.
5. What’s the .NET datatype that allows the retrieval of data by a unique key? HashTable.
6. What’s class SortedList underneath?
A sorted HashTable.
7. Will finally block get executed if the exception had not occurred?
Yes.
8. 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 {}.
9. 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.
10. 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.
11. What’s a delegate? A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.
12. What’s a multicast delegate? It’s a delegate that points to and eventually fires off several methods.
13. 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.
14. What are the ways to deploy an assembly? An MSI installer, a CAB archive, and XCOPY command.
15. 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.
16. What namespaces are necessary to create a localized application? System.Globalization, System.Resources.
17. What’s the difference between // comments, /* */ comments and /// comments? Single-line, multi-line and XML documentation comments.
18. How do you generate documentation from the C# file commented properly with a command-line compiler? Compile it with a /doc switch.
19. What’s the difference between c and code XML documentation tag?
Single line code example and multiple-line code example.
20. Is XML case-sensitive?
Yes, so
21. 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.
22. 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.
23. 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.
24. 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.
25. 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.
26. Where is the output of TextWriterTraceListener redirected? To the Console or a text file depending on the parameter passed to the constructor.
27. How do you debug an ASP.NET Web application? Attach the aspnet_wp.exe process to the DbgClr debugger.
28. 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).
29. 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.
30. Explain the three services model (three-tier application). Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
31. 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.
32. 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.
33. 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%’.
34. 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).
35. What connections does Microsoft SQL Server support? Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).
36. 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.
37. Why would you use untrusted verificaion? Web Services might use it, as well as non-Windows applications.
38. What does the parameter Initial Catalog define inside Connection String? The database name to connect to.
39. What’s the data provider name to connect to Access database? Microsoft.Access.
40. What does Dispose method do with the connection object? Deletes it from the memory.
41. 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.
A Hashtable object consists of buckets that contain the elements of the collection. A bucket is a virtual subgroup of elements within the Hashtable, which makes searching and retrieving easier and faster than in most collections. Each bucket is associated with a hash code, generated using a hash function and based on the key of the element.
The Dictionary class has the same functionality as the Hashtable class. A Dictionary of a specific type (other than Object) has better performance than a Hashtable for value types because the elements of Hashtable are of type Object and, therefore, boxing and unboxing typically occur if storing or retrieving a value type.
43.What is DLL Hell and how it is solved in .NET?
Windows
Registry cannot support the multiple versions of same com component
this is called the dll hell problem.
.net
solved using dll with different versions
Dll
hell problem is solved by dotnet it allows the application to specify
not only the library it needs to
run
but also the version of the assembly
44. What are Generic
Classes?
Generic classes are classes that
can hold objects of any class. Containers such as Lists, Arrays, Bags
and Sets are examples of generic classes.
Generic classes have type
parameters. Several separate classes in a C# program, each with a
different field type in them, can be replaced with a single generic
class. The generic class introduces a type parameter. This becomes
part of the class definition itself.
45. Why we use abstract
class?
If
some classes are having common behavior, instead of writing every
time the same thing in each class, write that in one class and ask
the other classes to use it[by making the classes as subclasses to
the abstract class].
this is nothing but inheritance. Abstract classes allow you to provide default functionality for the subclasses.
46. Database table to
collection.
List
list = dt.AsEnumerable().ToList();
or
IEnumerable
sequence = dt.AsEnumerable();
or
List
rows = table.Rows.Cast().ToList();
or
List
list = new List(dt.select());
47. What is the
difference between a deep copy and a shallow copy?
Shallow copies duplicate as little as possible. A shallow copy of a collection is a copy of the collection structure, not the elements. With a shallow copy, two collections now share the individual elements.
Deep copies duplicate everything. A deep copy of a collection is two collections with all of the elements in the original collection duplicated.
48. What is the
difference between const and static readonly?
The difference is that the value of a static readonly field is set at run time, and can thus be modified by the containing class, whereas the value of a const field is set to a compile time constant.
In the static readonly case, the containing class is allowed to modify it only
in the variable declaration (through a variable initializer)
in the static constructor (instance constructors, if it's not static)
static readonly is typically used if the type of the field is not allowed in a const declaration, or when the value is not known at compile time.
Instance readonly fields are also allowed.
Remember that for reference types, in both cases (static and instance) the readonly modifier only prevents you from assigning a new reference to the field. It specifically does not make immutable the object pointed to by the reference.
class Program {
public static readonly Test test = new Test();
static void Main(string[] args) {
test.Name = "Program";
test = new Test(); // Error: A static readonly field cannot be assigned to (except in a static constructor or a variable initializer)
}
}
class Test {
public string Name;
}
On the other hand, if Test were a value type, then assignment to test. Name would be an error.
49. Why use SP?
a.
It works/executes fast as it is in precompiled mode.
b. As it is
in the database so if the BL gets leaked there is no chance of
leaking the database… so security.
50. What are the
differences between stored procedure and functions in SQL Server
2000?
1) functions are used for computations whereas procedures can be used for performing business logic
2) functions MUST return a value, procedures need not be.
3) you can have DML(insert, update, delete) statements in a function. But, you cannot call such a function in a SQL
query..eg: suppose, if u have a function that is updating a table.. you can't call that function in any sql query.-
select myFunction(field) from sometable; will throw error.
4) function parameters are always IN, no OUT is possible
5) EXEC command can't be used inside a Function where it can be used inside an sproc
51. What do you
understand by Application Lifecycle Management (ALM)?
Abbreviated as ALM,
Application
Lifecycle
Management
refers to the capability to integrate, coordinate and manage the
different phases of the software delivery process. From development
to deployment, ALM is a set of pre-defined process and tools that
include definition, design, development, testing, deployment and
management. Throughout the ALM process, each of these steps are
closely monitored and controlled.
52. Diff b/w data
dictionary and hash table?
Basically Collections & Generics are useful in handling group of Objects.In .net,all the collections objects comes under the interface IEnumerable Which inturn has ArrayList(Index -Value)) & HashTable(Key- Value).After .net framework 2.0,ArrayList & HashTable were replaced with List & Dictionary .Now the Arraylist & HashTable are no more used in now a days projects.
Coming to difference between HashTable & Dictionary,Dictionary is generic whereas Hastable is not Generic.We can add any type of object to HashTable ,but while reteriving we need to Cast it to the required Type.So it is not type safe.But to dictionary,while declaring itself we can specify the type of Key & Value ,so no need to cast while retreiving.Let me explain it with an Example.
//HashTable
Program:
class
HashTableProgram
{
static
void
Main(string[]
args)
{
Hashtable
ht = new
Hashtable();
ht.Add(1,
"One");
ht.Add(2,
"Two");
ht.Add(3,
"Three");
foreach
(DictionaryEntry
de in
ht)
{
int
Key = (int)de.Key;
//Casting
string
value = de.Value.ToString(); //Casting
Console.WriteLine(Key
+ "
"
+ value);
}
}
}
//Dictionary
Example
class
DictionaryProgram
{
static
void
Main(string[]
args)
{
Dictionary<int,
string>
dt = new
Dictionary<int,
string>();
dt.Add(1,
"One");
dt.Add(2,
"Two");
dt.Add(3,
"Three");
foreach
(KeyValuePair<int,
String>
kv in
dt)
{
Console.WriteLine(kv.Key
+ "
"
+ kv.Value);
}
}
}
//In
Short
Simply,
Dictionary is a generic type, allowing:
static
typing (and compile-time verification)
use
without boxing
If you
are .NET 2.0 or above, you should prefer Dictionary
(and the other generic collections)
A
subtle but important difference is that Hashtable supports multiple
reader threads with a single writer thread, while Dictionary offers
no thread safety. If you need thread safety with a generic
dictionary, you must implement your own synchronization or (in .NET
4.0) use ConcurrentDictionary.
53. In
which event are the controls fully loaded?
Page
load event guarantees that all controls are fully loaded. Controls
are also accessed in Page_Init events but you will see that view
state is not fully loaded during this event
54. What is difference
between Trace and Debug?
Use Debug class to debug builds
- Use
Trace class for both debug and release builds.
55. How can you manage
client-side state?
Through Cookies
Through Hiddent field
Through ViewState
- Through
QueryString
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