C# Interview Questions

What is the difference between string keyword and System.String class?

Are string objects mutable or immutable?

What is a verbatim string literal and why do we use it?

string ImagePath = @"C:\Images\Buttons\SaveButton.jpg";
//Output: C:\Images\Buttons\SaveButton.jpg

string MultiLineText = @"This is multiline
Text written to be in
three lines.";
/* Output:
This is multiline
Text written to be in
three lines.
*/

string DoubleQuotesString = @"My Name is ""Pranaya.""";
//Output: My Name is "Pranaya."

What is the difference between System.Text.StringBuilder and System.String?

Difference between int and Int32 in C#

What's the limit on stack to store value types

1. Stack size: The default stack size for a 32-bit process in .NET is 1 MB, and for a 64-bit process it is 4 MB. This limits the total amount of memory that can be allocated on the stack.

2. Maximum stack allocation size: While the stack size is 1 MB or 4 MB, the maximum size of a single stack allocation is lower. The exact limit depends on the specific version of .NET, but is typically around 1-2 MB. Trying to allocate more than this will result in a StackOverflowException.

3. Numeric type limits: There are maximum and minimum values defined for each numeric value type in C#, based on the number of bits they use:
• sbyte: -128 to 127
• byte: 0 to 255
• short: -32,768 to 32,767
• ushort: 0 to 65,535
• int: -2,147,483,648 to 2,147,483,647
• uint: 0 to 4,294,967,295
• long: -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
• ulong: 0 to 18,446,744,073,709,551,615

4. Maximum string length: The maximum length of a string in C# is Int32.MaxValue, which is 2,147,483,647 characters. This limit is imposed by the .NET runtime due to memory constraints.

What are Access Modifiers in C#?

1. Public: The public type or member can be accessed by any other code in the same assembly or another assembly that references it.

2. Private: The type or member can only be accessed by code in the same class or struct.

3. Protected: The type or member can only be accessed by code in the same class or struct, or in a derived class.

4. Internal: The type or member can be accessed by any code in the same assembly, but not from another assembly.

5. Protected Internal: The type or member can be accessed by any code in the same assembly, or by any derived class in another assembly.

What is CLR

• Performance improvements.

• Language features such as inheritance, interfaces, and overloading for object-oriented programming.

• Garbage collection.

• Use of delegates instead of function pointers for increased type safety and security.

What is CTS?

What is the difference between a Queue and a Stack in .NET

What is the purpose of Generics in .NET

class DataStore<T>
{
	public T Data {get; set;}
}
DataStore<string> store = new DataStore<string>();

What is the difference between Deep Copy and Shallow Copy?

• Shallow Copy: A shallow copy creates a new object, but the fields of the new object reference the same memory locations as the original object. Changes to reference-type fields in the new object will affect the original object.

• Deep Copy: A deep copy creates a new object and recursively copies all the fields of the original object, including any referenced objects. The new object is entirely independent of the original.

What's the use of copy constructor

Key Uses of Copy Constructors

1. Object Duplication: Copy constructors allow you to create a new object that is a copy of an existing object. This is useful when you need to duplicate the state of an object for further processing without altering the original object.

2. Avoiding Side Effects: When working with mutable objects, changes made to the copied object should not affect the original object. A copy constructor ensures that the new object is independent of the original.

3. Encapsulation: By using a copy constructor, you can maintain proper encapsulation, avoiding direct manipulation of an object's internal state from outside the class.

4. Passing Objects by Value: When passing objects to methods, using a copy constructor can help ensure that the method works with a copy rather than the original object, preventing unintended modifications.

What's a private constructor?

1. Prevents external instantiation: Since a private constructor can only be accessed within the class, it prevents the creation of instances of the class from outside the class.

2. Used with static members: Private constructors are commonly used in classes that contain static members only. These classes are not meant to be instantiated.

3. Singleton pattern implementation: Private constructors are essential for implementing the Singleton pattern, which ensures that a class has only one instance.

4. Prevents automatic default constructor generation: If a class has only private constructors (with no parameters), the compiler will not generate a default constructor automatically.

5. Nested classes can access private constructors: While other classes cannot create instances of a class with a private constructor, nested classes can access the private constructor.

public class Singleton
{
    private static Singleton instance = null;

    private Singleton()
    {
        *// Private constructor to prevent external instantiation*
    }

    public static Singleton GetInstance()
    {
        if (instance == null)
        {
            instance = new Singleton();
        }
        return instance;
    }
}`

What’s the difference b/w a class with private constructor and static class?

Can “this” be used within a Static Method?

• No, “this” cannot be used within a static method.

• Because the keyword 'this' returns a reference to the current instance of the class containing it.

What is the use of the Yield keyword in C#?

Uses of the yield Keyword

1. Iterator Blocks: The yield keyword informs the compiler that the method in which it appears is an iterator block. This allows the method to return values one at a time, preserving the state between calls.

2. yield return: This statement is used to return the next value in the iteration. Each time the yield return statement is executed, the current location in the code is saved, and execution is paused until the next iteration is requested.
• Example:

public static IEnumerable<int> GetNumbers()
{
    for (int i = 0; i < 5; i++)
    {
        yield return i; // Returns the current value of i
    }
}

3. yield break: This statement is used to terminate the iteration. It signals that there are no more values to return, effectively ending the iteration early.
• Example:

public static IEnumerable<int> GetPositiveNumbers(IEnumerable<int> numbers)
{
    foreach (int number in numbers)
    {
        if (number < 0)
            yield break; // Stops iteration if a negative number is encountered
        yield return number; // Returns positive numbers
    }
}

4. Lazy Evaluation: The yield keyword allows for lazy evaluation of collections. This means that values are generated on-the-fly as they are requested, rather than being computed and stored all at once. This can lead to improved performance and reduced memory usage.

5. Stateful Iteration: With yield, you can maintain state across iterations without needing to manage the state explicitly. This makes it easier to create complex iteration logic.

What is a base keyword?

• The base keyword is used to access members of the base class from within a derived class.

• Call a method on the base class that has been overridden by another method.

• Specify which base-class constructor should be called when creating instances of the derived class.

• It is an error to use the base keyword from within a static method.