Interview Questions and Answers

Ques 1. Name 10 C# keywords.

abstract, event, new, struct, explicit, null, base, extern, object, this

Ques 2. What is public accessibility?

There are no access restrictions. All can access the public instance from anywhere.

Ques 3. What is private accessibility?

Access is restricted to within the containing class.

Ques 4. Class methods to should be marked with what keyword?

Static.

Ques 5. Does an object need to be made to run main?

No

Ques 6. Write a hello world console application.

using System;
namespace Console1
{
class Class1
{
[STAThread] // No longer needed
static void Main(string[] args)
{
Console.WriteLine("Hello world");
}
}
}

Ques 7. What is recursion?

Recursion is when a method calls itself.

Ques 8. What is a constructor?

A constructor performs initialisation for an object (including the struct type) or class.

Ques 9. What is a destructor?

A C# destuctor is not like a C++ destructor. It is actually an override for Finalize(). This
is called when the garbage collector discovers that the object is unreachable. Finalize()
is called before any memory is reclaimed.

Ques 10. Name 5 built in types.

Bool, char, int, byte, double

Ques 11. Is string Unicode, ASCII, or something else?

Unicode

Ques 12. Strings are immutable, what does this mean?

Any changes to that string are in fact copies.

Ques 13. Name a few string properties.

trim, tolower, toupper, concat, copy, insert, equals, compare.

Ques 14. What is boxing and unboxing?

Converting a value type (stack->heap) to a reference type (heap->stack), and viseversa.

Ques 15. Write some code to box and unbox a value type.

// Boxing
int i = 4;
object o = i;
// Unboxing
i = (int) o;

Ques 16. What is a heap and a stack?

There are 2 kinds of heap � 1: a chunk of memory where data is stored and 2: a tree
based data structure. When we talk about the heap and the stack we mean the first kind
of heap. The stack is a LIFO data structure that stores variables and flow control
information. Typically each thread will have its own stack.

Ques 17. What is a pointer?

A pointer is a reference to a memory address.

Ques 18. What does new do in terms of objects?

Initializes an object.

Ques 19. What is a struct?

Unlike in C++ a struct is not a class � it is a value type with certain restrictions. It is
usually best to use a struct to represent simple entities with a few variables. Like a Point
for example which contains variables x and y.

Ques 20. Describe 5 numeric value types ranges.

sbyte -128 to 127, byte 0 � 255, short -32,768 to 32,767, int -2,147,483,648 to
2,147,483,647, ulong 0 to 18,446,744,073,709,551,615

Ques 21. Write code for a case statement.

switch (n)
{
case 1:
x=1;
break;
case 2:
x=2;
break;
default:
goto case 1;
}

Ques 22. What is protected accessibility?

Access is restricted to types derived from the containing class.

Ques 23. What is protected internal accessibility?

Access is restricted to types derived from the containing class or from files within the same assembly.

Ques 24. What is the default accessibility for a class?

internal for a top level class, private for a nested one.

Ques 25. What is the default accessibility for members of an interface?

public

Ques 26. Methods must declare a return type, what is the keyword used when nothing is returned from the method?

Void

Ques 27. What is a reference parameter?

Reference parameters reference the original object whereas value parameters make a
local copy and do not affect the original. Some example code is shown:
using System;
namespace Console1
{
class Class1
{
static void Main(string[] args)
{
TestRef tr1 = new TestRef();
TestRef tr2 = new TestRef();
tr1.TestValue = "Original value";
tr2.TestValue = "Original value";
int tv1 = 1;
int tv2 = 1;
TestRefVal(ref tv1, tv2, ref tr1, tr2);
Console.WriteLine(tv1);
Console.WriteLine(tv2);
Console.WriteLine(tr1.TestValue);
Console.WriteLine(tr2.TestValue);
Console.ReadLine();
}
static public void TestRefVal(ref int tv1Parm,
int tv2Parm,
ref TestRef tr1Parm,
TestRef tr2Parm)
{
tv1Parm = 2;
tv2Parm = 2;
tr1Parm.TestValue = "New value";
tr2Parm.TestValue = "New value";
}
}
}
class TestRef
{
public string TestValue;
}
The output for this is:
2
1
New value
New value

Ques 28. What is an overloaded method?

An overloaded method has multiple signatures that are different.

Ques 29. If I have a constructor with a parameter, do I need to explicitly create a default constructor?

Yes

Ques 30. What is a delegate?

A delegate in C# is like a function pointer in C or C++. A delegate is a variable that calls
a method indirectly, without knowing its name. Delegates can point to static or/and
member functions. It is also possible to use a multicast delegate to point to multiple
functions.

Ques 31. Write some code to use a delegate.

Member function with a parameter
using System;
namespace Console1
{
class Class1
{
delegate void myDelegate(int parameter1);
static void Main(string[] args)
{
MyClass myInstance = new MyClass();
myDelegate d = new myDelegate(myInstance.AMethod);
d(1); // <--- Calling function without knowing its name.
Test2(d);
Console.ReadLine();
}
static void Test2(myDelegate d)
{
d(2); // <--- Calling function without knowing its name.
}
}
class MyClass
{
public void AMethod(int param1)
{
Console.WriteLine(param1);
}
}
}
Multicast delegate calling static and member functions
using System;
namespace Console1
{
class Class1
{
delegate void myDelegate(int parameter1);
static void AStaticMethod(int param1)
{
Console.WriteLine(param1);
}
static void Main(string[] args)
{
MyClass myInstance = new MyClass();
myDelegate d = null;
d += new myDelegate(myInstance.AMethod);
d += new myDelegate(AStaticMethod);
d(1); //both functions will be run.
Console.ReadLine();
}
}
class MyClass
{
public void AMethod(int param1)
{
Console.WriteLine(param1);
}
}
}

Ques 32. What is a value type and a reference type?

A reference type is known by a reference to a memory location on the heap.
A value type is directly stored in a memory location on the stack. A reference type is
essentially a pointer, dereferencing the pointer takes more time than directly accessing
the direct memory location of a value type.

Ques 33. string is an alias for what?

System.String

Ques 34. How do you dereference an object?

Set it equal to null.

Ques 35. In terms of references, how do == and != (not overridden) work?

They check to see if the references both point to the same object.

Ques 36. What is the default value for a bool?

False

Ques 37. Write code for an enumeration.

public enum animals {Dog=1,Cat,Bear};

Ques 38. Can a struct have methods?

Yes

Ques 39. What is checked { } and unchecked { }?

By default C# does not check for overflow (unless using constants), we can use
checked to raise an exception. E.g.:
static short x = 32767; // Max short value
static short y = 32767;
// Using a checked expression
public static int myMethodCh()
{
int z = 0;
try
{
z = checked((short)(x + y));
//z = (short)(x + y);
}
catch (System.OverflowException e)
{
System.Console.WriteLine(e.ToString());
}
return z; // Throws the exception OverflowException
}
This code will raise an exception, if we remove unchecked as in:
//z = checked((short)(x + y));
z = (short)(x + y);
Then the cast will raise no overflow exception and z will be assigned �2. unchecked can
be used in the opposite way, to say avoid compile time errors with constanst overflow.
E.g. the following will cause a compiler error:
const short x = 32767; // Max short value
const short y = 32767;
public static int myMethodUnch()
{
int z = (short)(x + y);
return z; // Returns -2
}
The following will not:
const short x = 32767; // Max short value
const short y = 32767;
public static int myMethodUnch()
{
int z = unchecked((short)(x + y));
return z; // Returns -2
}

Ques 40. Can assignment operators be overloaded directly?

No

Ques 41. What do operators is and as do?

as acts is like a cast but returns a null on conversion failure. Is comares an object to a
type and returns a boolean.

Ques 42. What is the difference between the new operator and modifier?

The new operator creates an instance of a class whereas the new modifier is used to
declare a method with the same name as a method in one of the parent classes.

Ques 43. Explain sizeof and typeof.

typeof obtains the System.Type object for a type and sizeof obtains the size of a type.

Ques 44. Contrast ++count vs. count++.

Some operators have temporal properties depending on their placement. E.g.
double x;
x = 2;
Console.Write(++x);
x = 2;
Console.Write(x++);
Console.Write(x);
Returns
323

Ques 45. .NET Stands for?

Ques 46. What is the default accessibility for members of a struct?

Private

Ques 47. Can the members of an interface be private?

No

Ques 48. A class can have many mains, how does this work?

Only one of them is run, that is the one marked (public) static, e.g:
public static void Main(string[] args)
{
//
// TODO: Add code to start application here
//
}
private void Main(string[] args, int i)
{
}

Ques 49. What are the two return types for main?

void and int

Ques 50. What is an out parameter?

An out parameter allows an instance of a parameter object to be made inside a method.
Reference parameters must be initialised but out gives a reference to an uninstanciated
object.

Ques 51. Write code to show how a method can accept a varying number of parameters.

using System;
namespace Console1
{
class Class1
{
static void Main(string[] args)
{
ParamsMethod(1,"example");
ParamsMethod(1,2,3,4);
Console.ReadLine();
}
static void ParamsMethod(params object[] list)
{
foreach (object o in list)
{
Console.WriteLine(o.ToString());
}
}
}
}

Ques 52. Can you use access modifiers with destructors?

No

Ques 53. What is a delegate useful for?

The main reason we use delegates is for use in event driven programming.

Ques 54. Are events synchronous of asynchronous?

Asynchronous

Ques 55. Events use a publisher/subscriber model. What is that?

Objects publish events to which other applications subscribe. When the publisher raises
an event all subscribers to that event are notified.

Ques 56. Can a subscriber subscribe to more than one publisher?

Yes, also - here's some code for a publisher with multiple subscribers.
using System;
namespace Console1
{
class Class1
{
delegate void myDelegate(int parameter1);
static event myDelegate myEvent;
static void AStaticMethod(int param1)
{
Console.WriteLine(param1);
}
static void Main(string[] args)
{
MyClass myInstance = new MyClass();
myEvent += new myDelegate(myInstance.AMethod);
myEvent += new myDelegate(AStaticMethod);
myEvent(1); //both functions will be run.
Console.ReadLine();
}
}
class MyClass
{
public void AMethod(int param1)
{
Console.WriteLine(param1);
}
}
}
Another example:
using System;
using System.Threading;
namespace EventExample
{
public class Clock
{
public delegate void TwoSecondsPassedHandler(object clockInstance,
TimeEventArgs time);
//The clock publishes an event that others subscribe to
public event TwoSecondsPassedHandler TwoSecondsPassed;
public void Start()
{
while(true)
{
Thread.Sleep(2000);
//Raise event
TwoSecondsPassed(this, new TimeEventArgs(1));
}
}
}
public class TimeEventArgs : EventArgs
{
public TimeEventArgs(int second)
{
seconds += second;
instanceSeconds = seconds;
}
private static int seconds;
public int instanceSeconds;
}
public class MainClass
{
static void Main(string[] args)
{
Clock cl = new Clock();
// add some subscribers
cl.TwoSecondsPassed += new
Clock.TwoSecondsPassedHandler(Subscriber1);
cl.TwoSecondsPassed += new
Clock.TwoSecondsPassedHandler(Subscriber2);
cl.Start();
Console.ReadLine();
}
public static void Subscriber1(object clockInstance, TimeEventArgs time)
{
Console.WriteLine("Subscriber1:" + time.instanceSeconds);
}
public static void Subscriber2(object clockInstance, TimeEventArgs time)
{
Console.WriteLine("Subscriber2:" + time.instanceSeconds);
}
}
}

Ques 57. Is a struct stored on the heap or stack?

Stack

Ques 58. Can C# have global overflow checking?

Yes

Ques 59. What is explicit vs. implicit conversion?

When converting from a smaller numeric type into a larger one the cast is implicit. An
example of when an explicit cast is needed is when a value may be truncated.

Ques 60. What doe the stackalloc operator do?

Allocate a block of memory on the stack (used in unsafe mode).