Q1. In which of these situations are interfaces better than abstract classes?

• When you need to define an object type's characteristics, use an interface. When you need to define an object type's capabilities, use an abstract class.
• Interfaces are a legacy of older versions of C#, and are interchangeable with the newer abstract class feature.
• When you need a list of capabilities and data that are classes-agnostic, use an interface. When you need a certain object type to share characteristics, use an abstract class.
• You should use both an interface and an abstract class when defining any complex object.

Q2. Which statement is true of delegates?

• Delegates are not supported in the current version of C#
• They cannot be used as callbacks.
• Only variables can be passed to delegates as parameters.
• They can be chained together.

Official documentation: Delegates

Q3. Which choice best defines C#'s asynchronous programming model?

• reactive
• inherited callback
• task-based
• callback-based

Official documentation: Task asynchronous programming model resposta correta --> var contacts = new List();

Q4. How would you determine if a class has a particular attribute?

• .

var type = typeof(SomeType);
var attribute = type.GetCustomAttribute<SomeAttribute>();

• .

var typeof(MyPresentationModel).Should().BeDecoratedWith<SomeAttribute>();

• .

Attribute.GetCustomAttribute, typeof(SubControllerActionToViewDataAttribute)

• .

Attribute.GetCustomAttribute(typeof(ExampleController), typeof(SubControllerActionToViewDataAttribute))

1. Official documentation: Attribute Class
2. Official documentation: Attribute.GetCustomAttribute Method

Q5. What is the difference between the ref and out keywords?

• Variables passed to specify that the parameter is an output parameter, while ref specifies that a variable may be passed to a function without being initialized.
• Variables passed to ref can be passed to a function without being initialized, while out specifies that the value is a reference value that can be changed inside the calling method.
• Variables passed to out can be passed to a function without being initialized, while ref specifies that the value is a reference value that can be changed inside the calling method.
• Variables passed to ref specify that the parameter is an output parameter, while out specifies that a variable may be passed to a function without being initialized.

1. Official documentation: ref
2. Official documentation: out parameter modifier

Q6. How could you retrieve information about a class, as well as create an instance at runtime?

• reflection
• serialization
• abstraction
• dependency injection

Official documentation: Reflection

Q7. What is this code an example of?

    private static object objA;
    private static object objB;

    private static void performTaskA()
    {
        lock (objB)
        {
            Thread.Sleep(1000);
            lock (objA) { }
        }
    }

    private static void PerformTaskB()
    {
        lock (objA)
        {
            lock (objB) { }
        }
    }

• a private class that uses multithreading
• multithread coding
• thread mismanagement
• a potential deadlock

Official documentation: Deadlocks and race conditions

Q8. What is the difference between an anonymous type and a regular data type?

• Anonymous types don't have type names
• Anonymous types can only be static
• Anonymous types can be used only in struts
• Anonymous types don't work with LINQ.

Official documentation: Anonymous Types

Q9. When would you use a Dictionary rather than an Array type in your application?

• When you need a jagged collection structure
• When you need to store values of the same type
• When you need to store key-value pairs rather than single values
• When you need an ordered, searchable list

Official documentation: Dictionary<TKey,TValue> Class

Q10. What is the difference between a.Equals(b) and a == b?

• The .Equals method compares reference identities while the == compares contents.
• The .Equals method compares primitive values while == compares all values.
• The .Equals method compares contents while == compares reference identity.
• The .Equals method compares reference types while == compares primitive value types

1. Official documentation: Object.Equals
2. c-sharpcorner: Equality Operator(==) vs .Equals()

Q11. Which choice best describes a deadlock situation?

• when you try to instantiate two objects at the same time in the same class or struct
• when you are trying to execute an action after a user event is registered
• when simultaneous instructions are waiting on each other to finish before executing
• when you try to execute a series of events simultaneously on multiple threads

Official documentation: Deadlocks and race conditions

Q12. How does the async keyword work?

• It allows access to asynchronous methods in the C# API
• It allows thread pooling and synchronous processes in static classes.
• It allows the await keyword to be used in a method
• It allows access to synchronous methods in the C# API

Official documentation: async

Q13. What is an object in C#?

• a class or struct, including its variables and functions
• a primitive data type that can be created only at compile time
• a value type that can be used only with an abstract class
• an instance of a class or struct that includes fields, properties, and/or methods

Official documentation: Objects

Q14. Which code snippet declares an anonymous type named userData?

• var<<!---->T> userData = new <<!---->T> { name = "John", age = 32 };
• var userData = new { name = "John", age = 32 };
• AType userData = new AType { name = "John", age = 32 };
• Anonymous<T> userData = new Anonymous<T> { name = "John", age = 32 };

Official documentation: Anonymous Types

Q15. What will be returned when this method is executed?

public void userInput(string charParameters) { }

• Nothing
• a Boolean
• a string variable
• an integer

Official documentation: void

Q16. In what order would the employee names in this example be printed to the console?

string[] employees = { "Joe", "Bob", "Carol", "Alice", "Will" };

IEnumerable<string> employeeQuery = from person in employees
                                    orderby person
                                    select person;

foreach(string employee in employeeQuery)
{
    Console.WriteLine(employee);
}

• ascending
• unordered
• descending
• first in, first out

dotnetpattern: LINQ OrderBy Operator

Q17. Lambda expressions are often used in tandem with which of the following?

• Namespaces
• LINQ
• Type Aliasing
• Assemblies

Official documentation: Language Integrated Query (LINQ) Overview

Q18. What is the correct formatting for single-line and multiline comments?

• /_/ - Single Line /_ - Multiline
• // Multiline /_ Single Line _/
• //* Multiline / Single Line
• // Single Line /* Multiline */

w3schools: C# Comments

Q19. How do you make a method in an abstract class overridable?

• Make it public
• Make it static
• Make it private
• Make it virtual

1. Official documentation: virtual
2. Official documentation: abstract

Q20. How would you write code for an integer property called Age with a getter and setter?

• public int Age { get - set }
• public int Age: get set;
• public int Age (get, set );
• public int Age { get; set; }

Official documentation: Using Properties

Q21. What is an abstract class?

• a class that is denoted by the class keyword (can be seen and used by any other class in the system--thus it is by default public)
• something denoted by the abstract keyword and used system-wide; if you want any program to create an object of a class you use the abstract class
• a class that is denoted by the virtual keyword
• a class that can be used only as a base class

Official documentation: Abstract and Sealed Classes and Class Members

Q22. When using a thread pool what happens to a given thread after it finishes its task?

• The thread is destroyed and memory is freed up.
• The thread runs in a loop until the next assignment.
• The thread goes inactive in the background and waits for garbage collection.
• The thread returns to the pool for reuse.

Official documentation: Thread pool characteristics

Q23. Which choice represents a class that inherits behavior from a base class?

• a second base class
• a revised class
• a derived class
• a parent class

Official documentation: Inheritance

Q24. What does operator overloading allow you to do?

• hide built-in operators when necessary
• add methods to be interpreted by the compiler at runtime
• define how enums and other primitive value types work within the rest of the application
• define custom functionality for common operators like addition and equality

Official documentation: Operator overloading

Q25. What is the main purpose of LINQ?

• to delete duplicate data
• to bind namespaces and assemblies
• to query and transform data
• to connect assemblies

Official documentation: Language Integrated Query (LINQ) Overview

Q26. What is the correct syntax for a new generic list of strings named contacts?

• public List contacts = new List();
• public List(string names) contacts = new List(string names)();
• var contacts = new List();
• var contacts = new List(string);

Official documentation: List Class

Q27. What is the difference between throw exceptions and throw clauses?

• Throw clauses fire only at runtime, while throw exceptions can fire at any time.
• Throw exceptions overwrite the stack trace, while throw clauses retain the stack information.
• Throw clauses overwrite the stack trace, while throw exceptions retain the stack information.
• Throw exceptions fire only at runtime, while throw clauses can fire during compile time.

1. Official documentation: throw
2. c-sharpcorner: Difference Between Throw Exception and Throw Clause

Q28. When an asynchronous method is executed, the code runs but nothing happens other than a compiler warning. What is most likely causing the method to not return anything?

• The return yield statement is missing at the end of the method.
• The method is missing an await keyword in its body.
• The wait keyword is missing from the end of the method.
• The yield keyword is missing from the method.

Official documentation: Starting tasks concurrently

Q29. What are C# events?

• system actions that communicate directly with the compiler at runtime
• actions that execute when the code compiles, generating logs and test output
• actions that generate notifications, which are sent to their registered listeners
• user-only methods that send data to the application's back end

Official documentation: Introduction to events

Q30. What kind of values can arrays store?

• unordered collections of numeric values
• key-value pairs of any C# supported type
• class and struct instances
• multiple variables, or collections, of the same type

Official documentation: Arrays

Q31. Given this enumeration, how would you access the integer-type value of 'AppState.Loading'?

enum AppState { OffLine, Loading, Ready }

• string currentState = (string)AppState.Loading;
• string currentState = AppState.Loading.integralVal;
• int currentState = AppState.Loading.rawValue;
• int currentState = (int)AppState.Loading;

Official documentation: Enumeration types

Q32. What character would you use to start a regular expression pattern at a word boundary?

• d
• \a
• \b
• \w

1. regular-expressions: Word Boundaries
2. Official documentation: Regular Expression Language - Quick Reference

Q33. To conform to the following interface, which of its members need to be implemented?

public interface INameable
{
    string FirstName { get; set; }
    string LastName { get; }
}

• Both the FirstName and LastName properties need to be implemented.
• Neither, they are both optional.
• Only the LastName property needs to be implemented.
• Only the FirstName property needs to be implemented.

Official documentation: interface

Q34. You're dealing with multiple assemblies in your program, but are worried about memory allocation. At what point in the program life cycle are assemblies loaded into memory?

• at runtime
• at compile time
• only when required
• only when programmatically loaded

1. Official documentation: Assembly Loading
2. Stackoverflow: When exactly are assemblies loaded?

Q35. What is the most accurate description of a regular expression?

• A regular expression is a C# tool used to parse HTML
• A regular expression is a special text string for describing a search pattern.
• A regular expression allows a variable to be passed by reference.
• A regular expression allows a class to conform to the Equatable protocol.

1. Official documentation: Regular Expression Language - Quick Reference
2. Official documentation: .NET regular expressions

Q36. Why would you use a class field in C#

• To define the behaviors of the class
• To hold information and data contained in the class object
• To communicate between classes and object
• To store the class definition value

Official documentation: Introduction to classes

Q37. When would you use generics in your code?

• to increase code performance
• all of these answers
• when code reuse is a priority
• when type safety is important

Official documentation: Generic classes and methods

Q38. What prints to the console when this code is executed?

public delegate void AuthCallback(bool validUser);
public static AuthCallback loginCallback = Login;
public static void Login()
{
    Console.WriteLine("Valid user!");
}

public static void Main(string[] args)
{
    loginCallback(true);
}

• Login successful...
• Valid user!
• an error, because the method signature of Login doesn't match the delegate
• Login successful... Valid user!

1. Official documentation: Introduction to Delegates
2. Official documentation: Introduction to Events

Q39. How would you declare a sealed class named User?

• public class User {}
• abstract User {}
• sealed class User {}
• private sealed class User {}

Official documentation: Abstract and Sealed Classes and Class Members

Q40. What is the difference between non-static and static classes?

• non-static classes need to be initialized before use, while static classes do not
• non-static classes are accessible only from an interface while static classes are accessible from anywhere
• non-static classes need to initialize all class members at runtime, while static classes do not
• non-static classes do not need to be initialized while static classes do

1. stackoverflow
2. Official documentation: Static Constructors

Q41. Which characteristic prevents this code from compiling?

public int age="28"

• type safety
• single inheritance
• dependency injection
• multiple inheritance

c-sharpcorner: Type Safety in .NET

Q42. How would you serialize this class?

public class User {}

• Mark the User class with the DeserializableAttribute.
• Declare the class as public serializable class User {}.
• Mark the User class with the SerializableAttribute attribute.
• Declare the class as private serializable class User {}.

Official documentation: SerializableAttribute Class

Q43. How would you write a delegate named ResultCallback with an int parameter named responseCode?

• public delegate ResultCallback(int responseCode);
• public delegate void ResultCallback<(int) responseCode>;
• public void delegate ResultCallback<int responseCode>;
• public delegate void ResultCallback(int responseCode);

Official documentation: Delegates

Q44. What is the difference between a static and non-static method?

• non-static methods always need to have a void return type
• non-static methods do not have access to static member variables
• static methods do not have to instantiate an instance of the class to call the method
• static methods always have to be public

Official documentation: Static Members

Q45. What is the correct way to write an event named apiResult based on a delegate named ResultCallback?

• public void event ResultCallback apiResult;
• public event ResultCallback(() -> apiResult);
• public event void ResultCallback
• public event ResultCallback apiResult;

Official documentation: Introduction to events

Q46. When will the code inside finally block be executed in a try-catch statement?

• if there is an error, it won't execute at all
• between the try and catch blocks
• after the try and catch blocks
• when the finally block overrides the catch block and executes in its place

Official documentation: try-catch

Q47. What method correctly extends the string class?

• public static string IsvalidName(this string i, string value) {}
• public static void IsvalidName(this string i, string value) {}
• public string IsvalidName(this string i, string value) {}
• public void IsvalidName(this string i, string value) {}

Q48. How are C# classes limited?

• They do not support multiple inheritance.
• They support multiple inheritance.
• They can have only a set number of properties.
• They can have only a set number of methods.

Official documentation: Class inheritance

Q49. What function do namespaces perform?

• Namespaces calculate code coverage at runtime.
• Namespaces compile application code together at compile time.
• Namespaces group code together into a single repository.
• Namespaces separate code into groupings, control access, and avoid naming collisions.

Official documentation: namespace

Q50. What is the correct way to write a public property with a private backing field?

• A

private int _password;
pubic int Password = { get; set; }

• B

private int _password;
public int Password = _password;

• C

private int _password;
public int Password
{
  get -> _password;
  set-> _password = value;
}

• D

private int _password;
public int Password
{
  get { return _password; }
  set { _password = value; }
}

Official documentation: Using Properties

Q51. What is a thread pool?

• a collection of synchronous methods created during initialization that cannot be reused
• a collection of threads created during initialization that can be reused
• a collection of threads only recognized at compile time that can be reused
• a collection of asynchronous methods created at compile time that cannot be reused

Official documentation: ThreadPool Class

Q52. When an object in C# is serialized, what is it converted to?

• XML
• JSON
• byte stream
• value stream

Official documentation: Serialization

Q53. What is a delegate

• a variable that holds a reference to a value type and its content
• a specific value type that can be used only in callback methods
• a type that holds a reference to a method with a particular parameter list and return type
• a custom variable type that can be used in abstract classes

Official documentation: Delegates

Q54. What are the four keywords associated with exception handling in C#?

• try, catch, valid, invalid
• try, valid, finally, throw
• try, catch, finally, throw
• finally, throw, valid, invalid

Tutorial Point

Q55. What is the main difference between the is and as operators?

• The is operator checks instance types, while the as operator checks the inherited type.
• The is operator checks primitive data types, while the as operator checks the object type.
• The as operator checks the object type, while the is operator attempts to cast an object to a specific type.
• The is operator checks the object type, while the as operator attempts to cast an object to a specific type.

Pluralsight guide

Q56. What is the difference between finally and finalize blocks?

• The finally block is called during the execution of a try and catch block, while the finalize method is called after garbage collection.
• The finally block is called after the execution of a try and catch block, while the finalize method is called just before garbage collection.
• The finalize block is called before the execution of a try and catch block, while the finally method is called just before garbage collection.
• The finalize block is called during the execution of a try and catch block, while the finally method is called after garbage collection.

C-sharpcorner

Q57. Your application has a value type called username that needs to be able to accept null values, but this is generating compile-time errors. How would you fix this in code?

• Null username = null;
• string? username = null;
• Type? username = null;
• Optional username = null;

Q58. Which code snippet correctly declares a custom exception named InvalidResponse?

• struct InvalidResponse: Exception {}
• class InvalidResponse: Exception {}
• public Exception InvalidResponse = new Exception ();
• public Exception InvalidResponse () -> Exception;

Official documentation: Exceptions

Q59. How would you write an enum variable called AppState with values for Offline, Loading, and Ready?

• enum AppState = [Offline, Loading, Ready]
• enum AppState {"Offline", "Loading", "Ready"}
• enum AppState = {Offline, Loading, Ready}
• enum AppState {Offline, Loading, Ready}

Official documentation: Enum

Q60. What is the main difference between a value type and a reference type?

• A value type can be any primitive type, while reference types must be type-agnostic.
• A value type refers to another value, while a reference type refers to a value in memory.
• A value type stores an actual value, while a reference type is a pointer to a value.
• A value type is available only at runtime, while a reference type is available only at compile time.

1. Official documentation: Value types
2. Official documentation: Reference types

Q61. What is the difference between the break and continue keywords?

• The break keyword is used to break out of multiple iteration statements, while continue can only break out of code blocks that have single iterations.
• The break keyword literally breaks out of a control flow statement, while continue ignores the rest of the control statement or iteration and starts the next one.
• The break keyword literally breaks out of the current control flow code and stops it dead, while continue keeps executing the code after an exception is thrown.
• The break keyword jumps out of an iteration and then proceeds with the rest of the control flow code, while continue stops the executing code dead.

Official documentation: Jump statements

Q62. Which code snippet correctly declares a variable named userId with a public get and private set?

• public int userID <get, set>;
• public int userID [get, private set];
• public int userID { get; private set; }
• public int userID = { public get, private set };

Official documentation: Properties

Q63. What is true about virtual methods?

• Overriding virtual methods in a derived class is mandatory.
• Overriding virtual methods in a derived class is not possible.
• Virtual methods always need a default implementation.
• Virtual methods cannot have a default implementation.

1. Official documentation: virtual
2. c-sharpcorner: Virtual Method in C#

Q64. What is likely to happen if you have multiple threads accessing the same resource in your program?

• resource overload
• thread jumping
• deadlock and race conditions
• nothing, since this is what threading is for

Official documentation: race conditions

Q65. How do you indicate that a string might be null?

• A string cannot be nullable.
• string? myVariable
• string myVariable = null
• string(null) myVariable

Official documentation: nullable value types

Q66. Do you need to declare an out variable before you use it?

• No, you can declare an out in the parameter list.
• No, Out variables are no longer part of C#.
• You must declare it if it is a primitive type.
• Yes.

Q67. How would you access the last two people in an array named People?

• People[..^2]
• You cannot do this in C#.
• People[..^3]
• People[^2]

Explain: You can do this in C#. However, none of the above answers are correct. You can access the last two items by using People[^2..]. Please see issue #3354 for more information. See also: Official Documentation: Ranges

Q68. When can anonymous types be created?

• at compile time
• after runtime
• at runtime
• after compile time

C-sharpcorner: Anonymous Types

Q69. What is true about thread multitasking?

• Thread multitasking allows code to be executed concurrently
• Thread multitasking allows code to be executed only when handling a user event.
• Thread multitasking blocks code from being executed simultaneously to guard memory.
• Thread multitasking adds single-threaded code blocks together.

Official Documentation: Threads

Q70. What accessibility level does this class field have?

private string LastName;

• It can be used by other code only in the same class or struct.
• It can be used by other code in a referenced assembly.
• It can be used only by code contained in a derived class.
• It can be used by other code in the same assembly.

Official Documentation: Accessibility Levels

Q71. How would you correctly declare a jagged array called 'partyInvites' with 10 empty elements?

• string[] partyInvites = new string[10];
• string[][] partyInvites = new string[10][];
• string[][] partyInvites = new string[10]();
• string <[]> partyInvites = new string <[10]>;

Official Documentation: Jagged Arrays

Q72. How could you pause a thread for three seconds?

• Thread.Pause(3000);
• Thread.Resume(-3000);
• Thread.Suspend(3000);
• Thread.Sleep(3000);

Reference

Q73. What is wrong with this code?

void MyFunction()
{
    {
        int a = 10;
        int b = 20;
        int c = a + b;
    }

    Console.WriteLine(c);
}

• Variable c is never used; displaying it on the console does not count as usage.
• Variables a and b are never used.
• You cannot place code inside brackets inside another block.
• Variable c no longer exists outside the block.

Reference

Q74. Which statement is True?

• All are true.
• None are true.
• string is a value type.
• string is an alias for String

Reference

Q75. How would you return more than one value from a method?

• Use either a tuple or an out variable.
• The only way is to use an out variable.
• The only way is to use a tuple.
• This cannot be done

Q76. Which is a valid example of a derived class?

• public class PremiumUser sub User {}
• public class PremiumUser: User {}
• public class PremiumUser -> sub User {}
• public class User: PremiumUser {}

Q77. What is the correct way to call a static method named DebugString from a static class called InputManager?

• static InputManager.DebugString();
• InputManager().DebugString;
• new InputManager().DebugString();
• InputManager.DebugString();

Q78. What values can be assigned to this variable?

public string? nickname

• null
• String values
• String values or null
• String values with more than one character

Q79. What is a destructor?

• a special called automatically whenever an object is created or updated
• an implicit method called automatically when thread pools are processed concurrently
• an explicit method called automatically when the compiler starts running
• a special method called automatically whenever an object is deleted or destroyed

Reference

Q80. Which code snippet correctly declares a CustomInt type alias of type Int32?

• typealias CustomInt = System.Int32;
• var<T> CustomInt = Int32;
• using CustomInt = System.Int32;
• type CustomInt = System<Int32>;

Reference

Q81. What is an enumeration type?

• an object of pass by reference type
• a value type that cannot hold constants
• set of named integral constants
• an object of pass-by-value type

Q82. What is the readonly keyword used for in-field declarations?

• to declare a member variable that cannot be calculated at runtime
• to declare a field whose value can be assigned only before the constructor exits
• to declare a static variable that must be set at compile time
• to declare a static variable that must be set at runtime

Q83. Which statement is true of C# methods?

• Methods store variables.
• Methods are actions that an object can take
• A method can be used only once per C# file.
• A method determines the state of a given property.

Official documentation: Methods (C# Programming Guide)

Q84 Which is a valid built-in C# Exception class?

• ArgumentNullValue
• InvalidFormatFoundException
• IndexOutOfPocket
• ArgumentNullException

Official documentation: ArgumentNullException Class

Q85. What is the purpose of an interface in C#?

• Interfaces are used to store data.
• Interfaces define a contract that classes must adhere to, specifying a set of methods and properties that implementing classes must provide.
• Interfaces are used to create instances of classes.
• Interfaces are used for code organization.

Official Documentation: Interfaces (C# Programming Guide)

Q86. What is the primary purpose of the finally block in a C# try-catch-finally statement?

• The finally block is used to handle exceptions.
• The finally block is used to define the main logic of the try-catch statement.
• The finally block is optional and not required in try-catch statements.
• The finally block is used to ensure that certain code is executed regardless of whether an exception occurs.

Official Documentation: try-catch (C# Reference)

Q87. Which data structure in C# allows you to store key-value pairs and is often used for quick data retrieval?

• ArrayList
• List
• Array
• Dictionary

Official Documentation: Dictionary<TKey, TValue> Class

Q88 The execution of the program begins with?

• Main()
• Get()
• Class()
• Display()

Q89 In C# 'using' is a?

• Class
• Directive
• Function
• Keyword