String Manipulation in C# 'Replace, Display Initials, and Modify Case'

using System;

class StringManipulation
{
    static void Main()
    {
        // Ask the user for input string
        Console.Write("Enter a string: ");
        string input = Console.ReadLine();
        
        // Replace lowercase 'a' with uppercase 'A' except if preceded by a space
        string replacedString = ReplaceLowercaseA(input);
        Console.WriteLine("Replaced String: " + replacedString);
        
        // Display initials (first letter and those after a space)
        string initials = GetInitials(input);
        Console.WriteLine("Initials: " + initials);
        
        // Display odd letters uppercase and even letters lowercase
        string modifiedString = ModifyCase(input);
        Console.WriteLine("Modified String (odd uppercase, even lowercase): " + modifiedString);
    }

    // Method to replace lowercase 'a' by uppercase 'A' unless preceded by a space
    static string ReplaceLowercaseA(string input)
    {
        char[] characters = input.ToCharArray();
        for (int i = 1; i < characters.Length; i++)
        {
            if (characters[i] == 'a' && characters[i - 1] != ' ')
            {
                characters[i] = 'A';
            }
        }
        return new string(characters);
    }

    // Method to get initials (first letter and those after a space)
    static string GetInitials(string input)
    {
        string[] words = input.Split(' ');
        string initials = "";
        
        foreach (var word in words)
        {
            if (word.Length > 0)
            {
                initials += word[0];
            }
        }
        
        return initials;
    }

    // Method to display odd letters uppercase and even letters lowercase
    static string ModifyCase(string input)
    {
        char[] characters = input.ToCharArray();
        
        for (int i = 0; i < characters.Length; i++)
        {
            if (i % 2 == 0)
            {
                characters[i] = Char.ToLower(characters[i]);
            }
            else
            {
                characters[i] = Char.ToUpper(characters[i]);
            }
        }
        
        return new string(characters);
    }
}

 Output

Enter a string: banana apple orange
Replaced String: bAnAnA apple orange
Initials: bao
Modified String (odd uppercase, even lowercase): bAnAnA ApPlE OrAnGe