C#

using System;
using System.Collections.Generic;

namespace Learning.Models;

public partial class Book
{
    public int BookId { get; set; }

    public string Title { get; set; } = null!;

    public string? Author { get; set; }

    public string? Isbn { get; set; }

    public int? PublishedYear { get; set; }
    
    public DateTime Date { get; set; }
    public string BookVersion { get; set; }

    public virtual ICollection<Rental> Rentals { get; set; } = new List<Rental>();

    public override string ToString()
    {
        return $"Title: {Title}, Author: {Author}, ISBN: {Isbn}";
    }
}

C#

using System;
using System.Collections.Generic;

namespace Learning.Models;

public partial class Book
{
    public int BookId { get; set; }

    public string Title { get; set; } = null!;

    public string? Author { get; set; }

    public string? Isbn { get; set; }

    public int? PublishedYear { get; set; }
    
    public DateTime Date { get; set; }
    public string BookVersion { get; set; }

    public virtual ICollection<Rental> Rentals { get; set; } = new List<Rental>();

    public override string ToString()
    {
        return $"Title: {Title}, Author: {Author}, ISBN: {Isbn}";
    }
}

C#
// Find nth term in fibonacci sequence - 0.1.1,...
Console.WriteLine(FibonacciFinder(5));
static int FibonacciFinder(int num)
{
    if (num is 1 or 2 or 3) return 1;
    else
    {
        return FibonacciFinder(num - 1) + FibonacciFinder(num - 2);
    }
}

C#
// Find nth term in fibonacci sequence - 0.1.1,...
Console.WriteLine(FibonacciFinder(5));
static int FibonacciFinder(int num)
{
    if (num is 1 or 2 or 3) return 1;
    else
    {
        return FibonacciFinder(num - 1) + FibonacciFinder(num - 2);
    }
}

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at DataStructure.LinkedLists`1.AddNode(T data) in C:\Users\...\RiderProjects\DataStructure\DataStructure\LinkedLists.cs:line 17
   at Program.<Main>$(String[] args) in C:\Users\...\RiderProjects\DataStructure\DataStructure\Program.cs:line 109

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at DataStructure.LinkedLists`1.AddNode(T data) in C:\Users\...\RiderProjects\DataStructure\DataStructure\LinkedLists.cs:line 17
   at Program.<Main>$(String[] args) in C:\Users\...\RiderProjects\DataStructure\DataStructure\Program.cs:line 109

C#
// Type parameter T in angle brackets.
public class GenericList<T>
{
    // The nested class is also generic, and
    // holds a data item of type T.
    private class Node(T t)
    {
        // T as property type.
        public T Data { get; set; } = t;

        public Node? Next { get; set; }
    }

    // First item in the linked list
    private Node? head;

    // T as parameter type.
    public void AddHead(T t)
    {
        Node n = new(t);
        n.Next = head;
        head = n;
    }

    // T in method return type.
    public IEnumerator<T> GetEnumerator()
    {
        Node? current = head;

        while (current is not null)
        {
            yield return current.Data;
            current = current.Next;
        }
    }
}

C#
// Type parameter T in angle brackets.
public class GenericList<T>
{
    // The nested class is also generic, and
    // holds a data item of type T.
    private class Node(T t)
    {
        // T as property type.
        public T Data { get; set; } = t;

        public Node? Next { get; set; }
    }

    // First item in the linked list
    private Node? head;

    // T as parameter type.
    public void AddHead(T t)
    {
        Node n = new(t);
        n.Next = head;
        head = n;
    }

    // T in method return type.
    public IEnumerator<T> GetEnumerator()
    {
        Node? current = head;

        while (current is not null)
        {
            yield return current.Data;
            current = current.Next;
        }
    }
}

C#
foreach (int i in ProduceEvenNumbers(9))
{
    Console.Write(i);
    Console.Write(" ");
}
// Output: 0 2 4 6 8

IEnumerable<int> ProduceEvenNumbers(int upto)
{
    for (int i = 0; i <= upto; i += 2)
    {
        yield return i;
    }
}

C#
foreach (int i in ProduceEvenNumbers(9))
{
    Console.Write(i);
    Console.Write(" ");
}
// Output: 0 2 4 6 8

IEnumerable<int> ProduceEvenNumbers(int upto)
{
    for (int i = 0; i <= upto; i += 2)
    {
        yield return i;
    }
}