using System;
using System.Text; // Required for StringBuilder

class Program
{
    static void Main()
    {
        // --- String Class Methods ---
        Console.WriteLine("=== String Class Methods ===");
        string str = "Hello World";

        Console.WriteLine("Original String: " + str);
        Console.WriteLine("To Upper Case: " + str.ToUpper());
        Console.WriteLine("To Lower Case: " + str.ToLower());
        Console.WriteLine("Substring (0,5): " + str.Substring(0, 5));
        Console.WriteLine("Replaced 'World' with 'C#': " + str.Replace("World", "C#"));
        Console.WriteLine("Contains 'Hello'? " + str.Contains("Hello"));
        Console.WriteLine("Length: " + str.Length);

        // --- StringBuilder Class Methods ---
        Console.WriteLine("\n=== StringBuilder Class Methods ===");
        StringBuilder sb = new StringBuilder("Hello");

        sb.Append(" World");
        Console.WriteLine("After Append: " + sb);

        sb.Insert(5, " C#");
        Console.WriteLine("After Insert: " + sb);

        sb.Replace("World", "Developers");
        Console.WriteLine("After Replace: " + sb);

        sb.Remove(5, 3);
        Console.WriteLine("After Remove: " + sb);

        sb.Clear();
        sb.Append("New String");
        Console.WriteLine("After Clear and Append: " + sb);
    }
}