C# Interview Questions, Part 1
1. What’s the implicit name of the parameter that gets passed into the class’ set method? Value, and its datatype depends on whatever variable we’re changing.
2. How do you inherit from a class in C#? Place a colon and then the name of the base class. Notice that it’s double colon in C++.
3. Does C# support multiple inheritance? No, use interfaces instead.
4. When you inherit a protected class-level variable, who is it available to? Classes in the same namespace.
5. Are private class-level variables inherited? Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.
6. Describe the accessibility modifier protected internal. It’s available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).
7. C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write? Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there’s no implementation in it.
8. What’s the top .NET class that everything is derived from? System.Object.
9. How’s method overriding different from overloading? When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.
10. What does the keyword virtual mean in the method definition? The method can be over-ridden.
11. Can you declare the override method static while the original method is non-static? No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.
12. Can you override private virtual methods? No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.
13. Can you prevent your class from being inherited and becoming a base class for some other classes? Yes, that’s what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName. It’s the same concept as final class in Java.
14. Can you allow class to be inherited, but prevent the method from being over-ridden? Yes, just leave the class public and make the method sealed.
15. What’s an abstract class? A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden. Essentially, it’s a blueprint for a class without any implementation.
16. When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)? When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden.
17. What’s an interface class? It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.
18. Why can’t you specify the accessibility modifier for methods inside the interface? They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it’s public by default.
19. Can you inherit multiple interfaces? Yes, why not.
20. And if they have conflicting method names? It’s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay.
C# interview questions and answers
I need to restrict a class by creating only one object throughout the application. How can I achieve this?
We can declare the constructor of the class as either protected or as private
int? d = 1; Type testType = d.GetType(); will result…
NOTE: This is objective type question, Please click question title for correct answer.
How can you make your machine shutdown from your program?
Process.Start("shutdown", "-s -f -t 0");
What is the use of unsafe keyword in C#?
In C# the value can be directly referenced to a variable, so there is no need of pointer. Use of pointer sometime crashes the application. But C# supports pointer, that means we can use pointer in C#.
The use of pointer in C# is defined as a unsafe code. So if we want to use pointer in C# the pointer must be present in the body of unsafe declaration. But pointer does not come under garbage collection.
Example:-
unsafe
{
int a, *b;
a = 25;
b = &a;
Console.WriteLine("b= {0}",b);//returns b= 25
}
What is difference between var and Dynamic ?
Var word was introduced with C#3.5(specifically for LINQ) while dynamic is introduced in C#4.0. variables declared with var keyword will get compiled and you can have all its related methods by intellisense while variables declared with dynamic keyword will never get compiled. All the exceptions related to dynamic type variables can only be caught at runtime.
What is dynamic keyword ?
Its newly introduced keyword of C#4.0. To indicate that all operations will be performed runtime.
What will happen if you declare a variable named "checked" with any data type?
Compiler will throw an error as checked is a keyword in C# So It cannot be used as variable name. Checked keyword is used to check the overflow arithmetic checking.
What are anonymous methods?
Anonymous methods are another way to declare delegates with inline code except named methods.
Restrictions of yield in try-catch.
While using yield keyword, mainly two restrictions are observed.
First is , we can’t use yield in finally.
Second is , we can’t place yield keyword in the catch block if try contains more than one catch blocks.
With yield break statement, control gets …
NOTE: This is objective type question, Please click question title for correct answer.
What first action compiler will take on detection of iterator ?
As soon as compiler will detect iterator, it will automatically generate current, MoveNext and Disposemethods of the IEnumerator or IEnumerator(T) type.
C# interview questions with answers
What are the different method parameter modifiers in C#?
out
ref
params
What are the different Iteration Constructs in C#?
for loop
foreach/in loop
while loop
do/while loop
What is the use of ?? operator in C#?
This operator allows you to assign a value to a nullable type if the retrieved value is in fact null.
What is the CIL representation of implicit and explicit keywords in C#?
The CIL representation is op_Implicit and op_Explicit respectively.
Which operators in C# provides automatic detection of arithmetic overflow and underflow conditions?
'checked' and 'unchecked' keywords provide automatic detection of arithmetic overflow and underflow conditions.
What is the use of stackalloc keyword in C#?
In an unsafe context it is used to allocate C# array directly on the stack.
Which keyword in C# is used to temporarily fix a variable so that its address may be found?
fixed keyword
What are the different C# preprocessor directives?
#region , #endregion :- Used to mark sections of code that can be collapsed.
#define , #undef :-Used to define and undefine conditional compilation symbols.
#if , #elif , #else , #endif :- These are used to conditionally skip sections of source code.
What is the use of GetInvocationList() in C# delegates?
GetInvocationList() returns an array of System.Delegate types, each representing a particular method that may be invoked.
C# delegate keyword is derived form which namespace?
C# delegate keyword is derived form System.MulticastDelegate.
What will be the length of string type variable which is just declared but not assigned any value?
As variable is not initialized and it is of reference type. So it's length will be null and it will throw a run time exception of "System.NullReferenceException" type, if used.
.Net Interview: Method and Property Questions
- What does the keyword “virtual” declare for a method or property?
The method or property can be overridden. - What’s the implicit name of the parameter that gets passed into the set method/property of a class?
Value. The data type of the value parameter is defined by whatever data type the property is declared as. - How is method overriding different from method overloading?
When overriding a method, you change the behavior of the method for the derived class. Overloading a method simply involves having another method with the same name within the class. - What are the different ways a method can be overloaded?
Different parameter data types, different number of parameters, different order of parameters. - If a base class has a number of overloaded constructors, and an inheriting class has a number of overloaded constructors; can you enforce a call from an inherited constructor to a specific base constructor?
Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class. - Can you declare an override method to be static if the original method is not static?
No. The signature of the virtual method must remain the same. (Note: Only the keyword virtual is changed to keyword override)
