Technical Interview Questions C#

Front 1

Is it possible to inline assembly or IL in C# code?

Back 1

No

Front 2

Is it possible to have different access modifiers on the get/set methods of a property?

Back 2

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.

Front 3

Is it possible to have a static indexer in C#?

Back 3

No. Static indexers are not allowed in C#.

Front 4

If I return out of a try/finally in C#, does the code in the finally-clause run?

Back 4

Yes. The code in the finally always runs. If you return out of the try block, or even if you do a “goto” out of the try, the finally block always runs

Front 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?

Back 5

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) { }

Front 6

How does one compare strings in C#?

Back 6

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

Front 7

How do you specify a custom attribute for the entire assembly (rather than for a class)?

Back 7

Global attributes must appear after any top-level using clauses and before the first type or namespace declarations. An example of this is as follows:

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

Note that in an IDE-created project, by convention, these attributes are placed in AssemblyInfo.cs.

Front 8

How do you mark a method obsolete?

Back 8

[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.

Front 9

How do you implement thread synchronization (Object.Wait, Notify,and CriticalSection) in C#?

Back 9

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);
}

Front 10

Name 10 C# keywords.

Back 10

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

Front 11

What is public accessibility?

Back 11

There are no access restrictions.

Front 12

What is protected accessibility?

Back 12

Access is restricted to types derived from the containing class.

Front 13

What is internal accessibility?

Back 13

A member marked internal is only accessible from files within the same assembly.

Front 14

What is protected internal accessibility?

Back 14

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

Front 15

What is private accessibility?

Back 15

Access is restricted to within the containing class.

Front 16

What is the default accessibility for a class?

Back 16

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

Front 17

What is the default accessibility for members of an interface?

Back 17

public

Front 18

What is the default accessibility for members of a struct?

Back 18

private

Front 19

Can the members of an interface be private?

Back 19

No

Front 20

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

Back 20

void

Front 21

Class methods to should be marked with what keyword?

Back 21

static

Front 22

Write some code using interfaces, virtual methods, and an abstract class.

Back 22

using System;

public interface Iexample1{
int MyMethod1();
}

public interface Iexample2
{
int MyMethod2();
}

public abstract class ABSExample : Iexample1, Iexample2{
public ABSExample(){
System.Console.WriteLine("ABSExample constructor");
}
public int MyMethod1(){
return 1;
}
public int MyMethod2(){
return 2;
}

public abstract void MyABSMethod();
}

public class VIRTExample : ABSExample{
public VIRTExample(){
System.Console.WriteLine("VIRTExample constructor");
}
public override void MyABSMethod(){
System.Console.WriteLine("Abstract method made concrete");
}

public virtual void VIRTMethod1(){
System.Console.WriteLine("VIRTMethod1 has NOT been overridden");
}
public virtual void VIRTMethod2(){
System.Console.WriteLine("VIRTMethod2 has NOT been overridden");
}
}

public class FinalClass : VIRTExample{
public override void VIRTMethod2(){
System.Console.WriteLine("VIRTMethod2 has been overridden");
}
}

Front 23

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

Back 23

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){
}

Front 24

Does an object need to be made to run main?

Back 24

No

Front 25

Write a hello world console application.

Back 25

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

}

}

Front 26

What are the two return types for main?

Back 26

void and int

Front 27

What is a reference parameter?

Back 27

Reference parameters reference the original object whereas value parameters make a local copy and do not affect the original.

Front 28

What is an out parameter?

Back 28

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.

Front 29

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

Back 29

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());
}
}
}
}

Front 30

What is an overloaded method?

Back 30

An overloaded method has multiple signatures that are different.

Front 31

What is recursion?

Back 31

Recursion is when a method calls itself.

Front 32

What is a constructor?

Back 32

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

Front 33

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

Back 33

Yes

Front 34

What is a destructor?

Back 34

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.

Front 35

Can you use access modifiers with destructors?

Back 35

No

Front 36

What is a delegate?

Back 36

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.

Front 37

Write some code to use a delegate.

Back 37

//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);
}
}
}

Front 38

What is a delegate useful for?

Back 38

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

Front 39

What is a value type and a reference type?

Back 39

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.

Front 40

Name 5 built in types.

Back 40

Bool, char, int, byte, double

Front 41

string is an alias for what?

Back 41

System.String

Front 42

Is string Unicode, ASCII, or something else?

Back 42

Unicode

Front 43

Strings are immutable, what does this mean?

Back 43

Any changes to that string are in fact copies.

Front 44

Name a few string properties.

Back 44

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

Front 45

What is boxing and unboxing?

Back 45

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

Front 46

Write some code to box and unbox a value type.

Back 46

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

Front 47

What is a heap and a stack?

Back 47

here 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.

Front 48

What is a pointer?

Back 48

A pointer is a reference to a memory address.

Front 49

What does new do in terms of objects?

Back 49

Initializes an object.

Front 50

How do you dereference an object?

Back 50

Set it equal to null.

Front 51

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

Back 51

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

Front 52

What is a struct?

Back 52

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.

Front 53

Describe 5 numeric value types ranges.

Back 53

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

Front 54

What is the default value for a bool?

Back 54

false

Front 55

Write code for an enumeration.

Back 55

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

Front 56

Write code for a case statement.

Back 56

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

Front 57

Is a struct stored on the heap or stack?

Back 57

Stack

Front 58

Can a struct have methods?

Back 58

Yes

Front 59

What is explicit vs. implicit conversion?

Back 59

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.

Front 60

Give examples of both explicit and implicit conversion.

Back 60

// Implicit
short shrt = 400;
int intgr = shrt;

// Explicit
shrt = (short) intgr;

Front 61

Can assignment operators be overloaded directly?

Back 61

No

Front 62

What do operators is and as do?

Back 62

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

Front 63

What is the difference between the new operator and modifier?

Back 63

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.

Front 64

Explain sizeof and typeof.

Back 64

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

Front 65

Contrast ++count vs. count++

Back 65

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

Front 66

What are the names of the three types of operators?

Back 66

Unary, binary, and conversion.

Front 67

An operator declaration must include a public and static modifier, can it have other modifiers?

Back 67

No

Front 68

Can operator parameters be reference parameters?

Back 68

No

Front 69

Arithmetic:
Logical (boolean and bitwise):
String concatenation:
Increment, decrement:
Shift:
Relational:
Assignment:
Member access:
Indexing:
Cast:
Conditional:
Delegate concatenation and removal:
Object creation:
Type information:
Overflow exception control:
Indirection and Address:

Back 69

Arithmetic: +
Logical (boolean and bitwise): &
String concatenation: +
Increment, decrement: ++
Shift: >>
Relational: ==
Assignment: =
Member access: .
Indexing: []
Cast: ()
Conditional: ?:
Delegate concatenation and removal: +
Object creation: new
Type information: as
Overflow exception control: checked
Indirection and Address: *

Front 70

What does operator order of precedence mean?

Back 70

Certain operators are evaluated before others. Brackets help to avoid confusion.

Front 71

What is special about the declaration of relational operators?

Back 71

Relational operators must be declared in pairs.

Front 72

What operators cannot be overloaded?

Back 72

=, ., ?:, ->, new, is, sizeof, typeof

Front 73

What is an exception?

Back 73

A runtime error.

Front 74

Can C# have multiple catch blocks?

Back 74

Yes

Front 75

Can break exit a finally block?

Back 75

No

Front 76

Can Continue exit a finally block?

Back 76

No

Front 77

What are expression and declaration statements?

Back 77

Expression – produces a value e.g. blah = 0
Declaration – e.g. int blah;

Front 78

A block contains a statement list {s1;s2;} what is an empty statement list?

Back 78

{;}

Front 79

What is a dangling else?

Back 79

if (n>0)
if (n2>0)
Console.Write("Dangling Else")
else

Front 80

Is switch case sensitive?

Back 80

Yes

Front 81

Write some code for a for loop.

Back 81

for (int i = 1; i <= 5; i++)
Console.WriteLine(i);

Front 82

Can you increment multiple variables in a for loop control?

Back 82

Yes
for (int i = 1; j = 2;i <= 5 ;i++ ;j=j+2)

Front 83

Write some code for a while loop.

Back 83

int n = 1;
while (n < 6){
Console.WriteLine("Current value of n is {0}", n);
n++;
}

Front 84

Write some code for do… while.

Back 84

int x;
int y = 0;

do{
x = y++;
Console.WriteLine(x);
}

while(y < 5);

Front 85

Write some code for a custom collection class.

Back 85

using System;
using System.Collections;

public class Items : IEnumerable{
private string[] contents;

public Items(string[] contents){
this.contents = contents;
}

public IEnumerator GetEnumerator(){
return new ItemsEnumerator(this);
}

private class ItemsEnumerator : IEnumerator{
private int location = -1;
private Items i;

public ItemsEnumerator(Items i){
this.i = i;
}

public bool MoveNext(){
if (location < i.contents.Length - 1){
location++;
return true;
}else{
return false;
}
}

public void Reset(){
location = -1;
}

public object Current{
get{return i.contents[location];}
}
}

static void Main(){
// Test
string[] myArray = {"a","b","c"};
Items items = new Items(myArray);

foreach (string item in items){
Console.WriteLine(item);
}

Console.ReadLine();
}
}

Front 86

Describe Jump statements: break, continue, and goto.

Back 86

Break terminates a loop or switch. Continue jumps to the next iteration of an enclosing iteration statement. Goto jumps to a labelled statement.

Front 87

How do you declare a constant?

Back 87

public const int c1 = 5;

Front 88

What is the default index of an array?

Back 88

0

Front 89

What is array rank?

Back 89

The dimension of the array.

Front 90

Can you resize an array at runtime?

Back 90

No

Front 91

Does the size of an array need to be defined at compile time.

Back 91

No

Front 92

Write some code to implement a multidimensional array.

Back 92

int[,] b = {{0, 1}, {2, 3}, {4, 5}, {6, 7}, {8, 9}};

Front 93

Write some code to implement a jagged array.

Back 93

// Declare the array of two elements:
int[][] myArray = new int[2][];

// Initialize the elements:
myArray[0] = new int[5] {1,3,5,7,9};
myArray[1] = new int[4] {2,4,6,8};

Front 94

What is an ArrayList?

Back 94

A data structure from System.Collections that can resize itself.

Front 95

Can an ArrayList be ReadOnly?

Back 95

Yes

Front 96

Write some code that uses an ArrayList.

Back 96

ArrayList list = new ArrayList();
list.Add("Hello");
list.Add("World");

Front 97

Can properties have an access modifier?

Back 97

Yes

Front 98

Can properties hide base class members of the same name?

Back 98

Yes

Front 99

What happens if you make a property static?

Back 99

They become class properties.

Front 100

Can a property be a ref or out parameter?

Back 100

A property is not classified as a variable – it can’t be ref or out parameter.

Front 101

What is an accessor?

Back 101

An accessor contains executable statements associated with getting or setting properties.

Front 102

Can an interface have properties?

Back 102

Yes

Front 103

What is early and late binding?

Back 103

Late binding is using System.object instead of explicitly declaring a class (which is early binding).

Front 104

What is polymorphism?

Back 104

Polymorphism is the ability to implement the same operation many times. Each derived method implements the operation inherited from the base class in its own way.

Front 105

What is a nested class?

Back 105

A class declare within a class.

Front 106

What is a namespace?

Back 106

A namespace declares a scope which is useful for organizing code and to distinguish one type from another.

Front 107

Can nested classes use any of the 5 types of accessibility?

Back 107

Yes

Front 108

Can base constructors can be private?

Back 108

Yes

Front 109

object is an alias for what?

Back 109

System.Object

Front 110

What is reflection?

Back 110

Reflection allows us to analyze an assembly’s metadata and it gives us a mechanism to do late binding.

Front 111

What namespace would you use for reflection?

Back 111

System.Reflection

Front 112

What does this do?
Public Foo() : this(12, 0, 0)

Back 112

Calls another constructor in the list

Front 113

Do local values get garbage collected?

Back 113

They die when they are pulled off the stack (go out of scope).

Front 114

Is object destruction deterministic?

Back 114

No

Front 115

Describe garbage collection (in simple terms).

Back 115

Garbage collection eliminates uneeded objects.
1. the new statement allocates memory for an object on the heap.
2. When no objects reference the object it may be removed from the heap (this is a non deterministic process).
3. Finalize is called just before the memory is released.

Front 116

What is the using statement for?

Back 116

The using statement defines a scope at the end of which an object will be disposed.

Front 117

How do you refer to a member in the base class?

Back 117

To refer to a member in the base class use:return base.NameOfMethod().

Front 118

Can you derive from a struct?

Back 118

No

Front 119

Does C# supports multiple inheritance?

Back 119

No

Front 120

The C# keyword ‘int’ maps to which .NET type?

Back 120

System.Int32

Front 121

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”;

Back 121

3. string s = @”n Test string”;

Front 122

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;

Back 122

1.int[,] myArray;

Front 123

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.

Back 123

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

Front 124

What is boxing?

1) Encapsulating an object in a value type.
2) Encapsulating a copy of an object in a value type.
3) Encapsulating a value type in an object.
4) Encapsulating a copy of a value type in an object.

Back 124

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

Front 125

All classes derive from what?

Back 125

System.Object

Front 126

Is constructor or destructor inheritance explicit or implicit? What does this mean?

Back 126

Constructor or destructor inheritance is explicit…. Public Extended : base()à this is called the constructor initializer.

Front 127

Can different assemblies share internal access?

Back 127

No

Front 128

Can you inherit from multiple interfaces?

Back 128

Yes

Front 129

In terms of constructors, what is the difference between: public MyDerived() : base() an public MyDerived() in a child class?

Back 129

Nothing

Front 130

Can abstract methods override virtual methods?

Back 130

Yes

Front 131

What keyword would you use for scope name clashes?

Back 131

this

Front 132

Can you have nested namespaces?

Back 132

Yes

Front 133

What are attributes?

Back 133

Attributes are declarative tags which can be used to mark certain entities (like methods for example).

Front 134

Name 3 categories of predefined attributes.

Back 134

COM Interop, Transaction, Visual Designer Component Builder