Welcome to this introductory lesson focused on List Operations without the use of built-in functions. While C# provides powerful methods within its collections, specifically List<T>, to simplify list operations, understanding the concepts behind these key functions significantly improves your ability to solve complex problems. It also prepares you for scenarios where built-in methods may not exist, or if they do, may not offer the optimal solution.

Understanding list operations in C# begins with grasping List<T>. As straightforward as it might seem, conducting operations on a List<T> without using built-in methods involves organizing and processing the elements manually. This may include counting the occurrences of specific elements, finding the index of an element, or reversing the list. Careful navigation and precise control over how elements in the list are accessed or manipulated are key to effective list operation.

Here is a code snippet that counts the number of occurrences of a specific element in a List<T>:

C#
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1using System;
2using System.Collections.Generic;
3
4public class Solution
5{
6    public int CountOccurrences(List<int> list, int target)
7    {
8        int count = 0;
9        for (int i = 0; i < list.Count; i++)
10        {
11            if (list[i] == target)
12            {
13                count++;
14            }
15        }
16        return count;
17    }
18
19    public static void Main(string[] args)
20    {
21        Solution solution = new Solution();
22        List<int> list = new List<int> { 1, 2, 3, 2, 4, 2 };
23
24        // Example usage
25        int count = solution.CountOccurrences(list, 2);
26        Console.WriteLine("Element 2 appears " + count + " times."); // Outputs: Element 2 appears 3 times.
27    }
28}

Grasping the concepts covered in this instruction is critical to succeeding in the practice exercises that follow, so take the time to understand these concepts thoroughly. Remember, we're not just learning algorithms but cultivating a deeper understanding of how we can break down and solve complex problems with relatively simple code. Therefore, get ready and anticipate an exciting and revealing practice session!