---
tags: Linkedin-skill
disqus: HackMD
---
# C# Test

## C#

#### 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.
- [x] 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.
- [x] You should use both an interface and an abstract class when defining any complex object.

#### Q2. Which statement is true of delegates?

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

[Official documentation: Delegates](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/delegates/#delegates-overview)

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

- [ ] reactive
- [ ] inherited callback
- [x] task-based
- [ ] callback-based

[Official documentation: Task asynchronous programming model](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/async/task-asynchronous-programming-model) resposta correta --> var contacts = new List<string>();

#### 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)

- [x] .

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

1. [Official documentation: Attribute Class](https://docs.microsoft.com/en-us/dotnet/api/system.attribute?view=net-5.0)
2. [Official documentation: Attribute.GetCustomAttribute Method](https://docs.microsoft.com/en-us/dotnet/api/system.attribute.getcustomattribute?view=net-5.0)

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

- [ ] Variables passed to out 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.
- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/ref)
2. [Official documentation: out parameter modifier](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/out-parameter-modifier)

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

- [x] reflection
- [ ] serialization
- [ ] abstraction
- [ ] dependency injection

[Official documentation: Reflection ](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/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
- [x] a potential deadlock

[Official documentation: Deadlocks and race conditions](https://docs.microsoft.com/en-us/dotnet/standard/threading/managed-threading-best-practices#deadlocks-and-race-conditions)

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

- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/types/anonymous-types)

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

- [ ] when you need a jagged collection structure
- [ ] when you need to store values of the same type
- [x] 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](https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2?view=net-5.0)

#### 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.
- [x] The .Equals method compares contents while `==` compares reference identity.
- [ ] The .Equals method compares reference type while `==` compares primitive value types

1. [Official documentation: Object.Equals](https://docs.microsoft.com/en-us/dotnet/api/system.object.equals)
2. [c-sharpcorner: Equality Operator(==) vs .Equals()](https://www.c-sharpcorner.com/UploadFile/3d39b4/difference-between-operator-and-equals-method-in-C-Sharp)

#### 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
- [x] 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](https://docs.microsoft.com/en-us/dotnet/standard/threading/managed-threading-best-practices#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.
- [x] It allows the await keyword to be used in a method
- [ ] It allows access to synchronous methods in the C# API

[Official documentation: async](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/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
- [x] an instance of a class or struct that includes fields, properties, and/or methods

[Official documentation: Objects](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/object-oriented/objects)

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

- [ ] `var<<!---->T> userData = new <<!---->T> { name = "John", age = 32 };`
- [x] `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](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/types/anonymous-types)

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

`public void userInput(string charParameters) { }`

- [x] nothing
- [ ] a Boolean
- [ ] a string variable
- [ ] an integer

[Official documentation: void](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/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);
}

- [x] ascending
- [ ] unordered
- [ ] descending
- [ ] first in, first out

[dotnetpattern: LINQ OrderBy Operator](http://dotnetpattern.com/linq-orderby-operator)

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

- [ ] Namespaces
- [x] LINQ
- [ ] Type Aliasing
- [ ] Assemblies

[Official documentation: Language Integrated Query (LINQ) Overview](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/linq/)

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

- [ ] `/_/ - Single Line`
`/_ - Multiline`
- [ ] `// Multiline`
`/_ Single Line _/`
- [ ] `//\* Multiline`
`/ Single Line`
- [x] `// Single Line`
`/* Multiline */`

[w3schools: C# Comments](https://www.w3schools.com/cs/cs_comments.php)

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

- [ ] Make it public
- [ ] Make it static
- [ ] Make it private
- [x] Make it virtual

1. [Official documentation: virtual](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/virtual)
2. [Official documentation: abstract](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/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 );
- [x] public int Age { get; set; }

[Official documentation: Using Properties](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/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
- [x] a class that can be used only as base class

[Official documentation: Abstract and Sealed Classes and Class Members](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/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 loop until the next assignment.
- [ ] The thread goes inactive in the background and waits for garbage collection.
- [x] The thread returns to the pool for reuse.

[Official documentation: Thread pool characteristics](https://docs.microsoft.com/en-us/dotnet/standard/threading/the-managed-thread-pool#thread-pool-characteristics)

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

- [ ] a second base class
- [ ] a revised class
- [x] a derived class
- [ ] a parent class

[Official documentation: Inheritance](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/object-oriented/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
- [x] define custom functionality for common operators like addition and equality

[Official documentation: Operator overloading](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/operator-overloading)

#### Q25. What is the main purpose of LINQ?

- [ ] to delete duplicate data
- [ ] to bind namespaces and assemblies
- [x] to query and transform data
- [ ] to connect assemblies

[Official documentation: Language Integrated Query (LINQ) Overview](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/linq/#query-expression-overview)

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

- [ ] public List<string names> contacts = new List<string names>();
- [ ] public List(string names) contacts = new List(string names)();
- [x] var contacts = new List<string>();
- [ ] var contacts = new List(string);

[Official documentation: List<T> Class](https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1?view=net-5.0)

#### 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.
- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/throw)
2. [c-sharpcorner: Difference Between Throw Exception and Throw Clause](https://www.c-sharpcorner.com/UploadFile/akkiraju/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.
- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/async/#start-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
- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/events-overview)

#### 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
- [x] multiple variables, or collections, of the same type

[Official documentation: Arrays](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/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;
- [x] int currentState = (int)AppState.Loading;

[Official documentation: Enumeration types](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/enum#conversions)

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

- [ ] d
- [ ] \a
- [x] \b
- [ ] \w

1. [regular-expressions: Word Boundaries](https://www.regular-expressions.info/wordboundaries.html)
2. [Official documentation: Regular Expression Language - Quick Reference](https://docs.microsoft.com/en-us/dotnet/standard/base-types/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; }
}

- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/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
- [x] only when required
- [ ] only when programmatically loaded

1. [Official documentation: Assembly Loading](https://docs.microsoft.com/en-us/dotnet/framework/deployment/best-practices-for-assembly-loading)
2. [Stackoverflow : When exactly are assemblies loaded?](https://stackoverflow.com/questions/21914692/when-exactly-are-assemblies-loaded)

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

- [ ] A regular expression is a C# tool used to parse HTML
- [x] A regular expression is a special text string for describing a search patters.
- [ ] 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](https://docs.microsoft.com/en-us/dotnet/standard/base-types/regular-expression-language-quick-reference)
2. [Official documentation: .NET regular expressions](https://docs.microsoft.com/en-us/dotnet/standard/base-types/regular-expressions)

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

- [ ] To define behaviours of the class
- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/types/classes)

#### Q37. When would you use generics in your code?

- [ ] to increase code performance
- [x] all of these answers
- [ ] when code reuse is a priority
- [ ] when type safety is important

[Official documentation: Generic classes and methods](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/types/generics)

#### 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!
- [x] an error, because the method signature of Login doesn't match the delegate
- [ ] Login successful... Valid user!

1. [Official documentation: Introduction to Delegates](https://docs.microsoft.com/en-us/dotnet/csharp/delegates-overview)
2. [Official documentation: Introduction to Events](https://docs.microsoft.com/en-us/dotnet/csharp/events-overview)

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

- [ ] public class User {}
- [ ] abstract User {}
- [x] sealed class User {}
- [ ] private sealed class User {}

[Official documentation: Abstract and Sealed Classes and Class Members](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/abstract-and-sealed-classes-and-class-members)

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

- [x] 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](https://stackoverflow.com/questions/20451554/whats-the-function-of-a-static-constructor-in-a-non-static-class)
2. [Official documentation: Static Constructors](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/static-constructors)

#### Q41. Which characteristic prevents this code from compiling?

`public int age="28"`

- [x] type safety
- [ ] single inheritance
- [ ] dependency injection
- [ ] multiple inheritance

[c-sharpcorner: Type Safety in .NET](https://www.c-sharpcorner.com/UploadFile/vikie4u/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 {}`.
- [x] Mark the User class with the `SerializableAttribute` attribute.
- [ ] Declare the class as `private serializable class User {}`.

[Official documentation: SerializableAttribute Class](https://docs.microsoft.com/en-us/dotnet/api/system.serializableattribute?view=net-5.0)

#### 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\>;
- [x] public delegate void ResultCallback(int responseCode);

[Official documentation: Delegates](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/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
- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/static-classes-and-static-class-members#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
- [x] public event ResultCallback apiResult;

[Official documentation: Introduction to events](https://docs.microsoft.com/en-us/dotnet/csharp/events-overview)

#### 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
- [x] after the try and catch blocks
- [ ] when the finally block overrides the catch block and executes in its place

[Official documentation: try-catch](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/try-catch)

#### Q47. What method correctly extends the string class?

- [x] 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?

- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/types/classes#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.
- [x] Namespaces separate code into groupings, control access, and void naming collisions.

[Official documentation: namespace](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/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;
}

- [x] D

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

[Official documentation: Using Properties](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/using-properties)

#### Q51. What is a thread pool?

- [ ] a collection of synchronous methods created during initialization that cannot be reused
- [x] 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](https://docs.microsoft.com/en-us/dotnet/api/system.threading.threadpool?view=net-5.0)

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

- [ ] XML
- [ ] JSON
- [x] byte stream
- [ ] value stream

[Official documentation: Serialization](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/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
- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/delegates/)

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

- [ ] try, catch, valid, invalid
- [ ] try, valid, finally, throw
- [x] try, catch, finally, throw
- [ ] finally, throw, valid, invalid

[Tutorial Point](https://www.tutorialspoint.com/csharp/csharp_exception_handling.htm#:~:text=Exceptions%20provide%20a%20way%20to,catch%2C%20finally%2C%20and%20throw.)

#### 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 object type, while the is operator attempts to cast an object to a specific type.
- [x] The is operator checks object type, while the as operator attempts to cast an object to a specific type.

[Pluralsight guide](https://www.pluralsight.com/guides/csharp-is-as-operators-is-expressions)

#### 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.
- [x] 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](https://www.c-sharpcorner.com/forums/final-finally-and-finalize)

#### 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<string> username = null;
- [x] string? username = null;
- [ ] Type<string>? username = null;
- [ ] Optional<string> username = null;

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

- [ ] struct InvalidResponse: Exception {}
- [x] class InvalidResponse: Exception {}
- [ ] public Exception InvalidResponse = new Exception ();
- [ ] public Exception InvalidResponse () -> Exception;

[Official documentation: Exceptions](https://docs.microsoft.com/en-us/dotnet/standard/exceptions/how-to-create-user-defined-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}
- [x] enum AppState {Offline, Loading, Ready}

[Official documentation: Enum](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/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.
- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/value-types)
2. [Official documentation: Reference types](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/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.
- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/statements/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];`
- [x] `public int userID { get; private set; }`
- [ ] `public int userID = { public get, private set };`

[Official documentation: Properties](https://docs.microsoft.com/en-us/dotnet/csharp/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.`
- [x] `Virtual methods always need a default implementation.`
- [ ] `Virtual methods cannot have default implementation.`

1. [Official documentation: virtual](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/virtual)
2. [c-sharpcorner: Virtual Method in C#](https://www.c-sharpcorner.com/UploadFile/3d39b4/virtual-method-in-C-Sharp/)

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

- [ ] `resource overload`
- [ ] `thread jumping`
- [x] `deadlock and race conditions`
- [ ] `nothing, since this is what threading is for`

[Official documentation: race conditions](https://docs.microsoft.com/en-us/archive/msdn-magazine/2008/october/concurrency-hazards-solving-problems-in-your-multithreaded-code)

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

- [ ] `A string cannot be nullable.`
- [x] `string? myVariable`
- [ ] `string myVariable = null`
- [ ] `string(null) myVariable`

[Official documentation: nullable value types](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/nullable-value-types#declaration-and-assignment)

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

- [x] `No, you can declare an out in the parameter list.`
- [ ] `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?

- [x] `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 could access the last two items by using `People[^2..]`. Please see [issue #3354](https://github.com/Ebazhanov/linkedin-skill-assessments-quizzes/issues/3354) for more information.
See also: [Official Documentation: Ranges](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/ranges)

#### Q68. When can anonymous types be created?

- [x] `at compile time`
- [ ] `after runtime`
- [ ] `at runtime`
- [ ] `after compile time`

[C-sharpcorner: Anonymous Types](https://www.c-sharpcorner.com/UploadFile/ff2f08/anonymous-types-in-C-Sharp/)

#### Q69. What is true about thread multitasking?

- [x] `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](https://docs.microsoft.com/en-us/dotnet/standard/threading/threads-and-threading)

#### Q70. What accessibility level does this class field have ?

`private string LastName;`

- [x] 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](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/accessibility-levels)

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

- [ ] `string[] partyInvites = new string[10];`
- [x] `string[][] partyInvites = new string[10][];`
- [ ] `string[][] partyInvites = new string[10]();`
- [ ] `string <[]> partyInvites = new string <[10]>;`

[Official Documentation: Jagged Arrays](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/arrays/jagged-arrays)

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

- [ ] Thread.Pause(3000);
- [ ] Thread.Resume(-3000);
- [ ] Thread.Suspend(3000);
- [x] Thread.Sleep(3000);

[Reference](https://docs.microsoft.com/en-us/dotnet/api/system.threading.thread.sleep?view=net-6.0)

#### 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.
- [x] Variable c no longer exists outside the block.

[Reference](https://stackoverflow.com/a/6136865)

#### Q74. Which statement is True?

- [ ] All are true.
- [ ] None are true.
- [ ] string is a value type.
- [x] string is an alias for String

[Reference](https://stackoverflow.com/q/7074)

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

- [x] 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 {}`
- [x] `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();`
- [x] `InputManager.DebugString();`

#### Q78. What values can be assigned to this variable?

public string? nickname

- [ ] null
- [ ] String values
- [x] String values or null
- [ ] String values with more than one character