C# Interview questions and answers for freshers and experienced - Part One

Hello friend, in this post I am sharing some C# interview questions with their answers. I had shared advanced level interview questions before this but most of my friends has asking me about some interview questions for freshers and experience range of 1-3 years so have decided to share some with this series. Hope you will get benefited.

Can we declare string variables like below?

string a,b,c = string.Empty;

If yes then what will be the value of a,b and c?

Yes it is possible to declare variables in above way.
Many developers has habit of declaring each variable separately so sometime they gets confused after seeing code like this.
Coming to the sub question what will the values of a,b and c.  In above case c will have string.Empty value on the other hand a & b will have null value as we haven't set any for those. All will have string.Empty value if you had set like below

string a = string.Empty,b=sting.Empty,c=string.Empty;

What is faster a Class or Structure?

When it comes to the difference between class and structure you know Class is reference type and structure is value type but when it comes to the which is faster among them then there is long discussion and most of the time no confirmed output.

To answer this question, as struct is a value type it gets allocated on stack or inline in containing types so if we consider struct independently then it is faster to instantiate & to destroy as compare to class which gets allocated on heap.

In my point of view when to use which is more important and it depends on some other considerations such as size of type, its logical representation,frequency of it being get boxed,mutable or immutable etc.
I will recommend reading this post on MSDN to have more idea on choosing between class and struct.

Which Constructor gets called first ? Parent Class or child class?

This is very basic question now days but still has capability to confuse freshers during interviews. Coming to the answer, Base class constructor always gets called first and rather memorizing it you can think it like you have derived class to add some more functionality to the base class so to add something you need a base similar case is with this too.

Point to note, though base class constructor gets called first derived class initializer gets called before base class initializer. Same case with destructor too, dervied class destructor gets invoked before the base class destructor.
 

Use of ? in C#

You might be using ? in your code many times but when it gets specifically asked what is the use of ? in C# then sometimes you not able to recall which makes this as an interview question.
Coming to the answer. Below are soem usage of "?" in C#

Nullable type :

To declare a nullable type ? is gets used.
e.g. 

int? num = null;

Nullable types are instances of the System.Nullable<T> struct. A nullable type can represent the correct range of values for its underlying value type, plus an additional null value.

To know more about Nullable Type,read this MSDN post.

?? Operator (null-coalescing operator) which returns the left-hand operand if the operand is not null; otherwise it returns the right hand operand. It mostly gets used with nullable types.

int? x = null;
int y = x ?? -1;

In above example if x is null then y will have -1 value else x's value.

Conditional operator (?:)

? gets used in conditional operator which returns one of two values depending on the value of a Boolean expression.

int i = 6;
string str = (i >3 ? "yes": "no");

In above example conditional operator is used. So if i > 3 condition is true str will have value "yes" else value "no"

What is the use of "using" statement in c#?

The "using" statement provides convenient syntax that ensures the correct use of IDisposable objects. Within the using block, the object is read-only and cannot be modified or reassigned.

To use "using" statement for particular type it must implement IDisposable interface. When you use "using" statement.

When you wrap a IDisposable objects with using statement compiler converts it to try....finally block and object gets disposed in finally block. Read more about it here.

Let me know your thoughts about above questions in comment section below. Thanks.

Go to Part Two