Strings manipulation C# Exercise - C# Programming Course

using System;  // Importing the System namespace to use its functionality

class Program  // Define the main class
{
    static void Main()  // The entry point of the program
    {
        Console.Write("Enter a string: ");  // Prompt the user to input a string
        string input = Console.ReadLine();  // Read the input from the user

        // Call the methods to manipulate and display the string
        string replacedString = ReplaceLowercaseA(input);
        string initials = GetInitials(input);
        string oddEvenString = OddEvenCase(input);

        // Display all the manipulated strings
        Console.WriteLine($"Replaced String: {replacedString}");  // Display the string with replaced characters
        Console.WriteLine($"Initials: {initials}");  // Display the initials
        Console.WriteLine($"Odd/Even Case: {oddEvenString}");  // Display the odd/even case transformation
    }

    // Method to replace all lowercase 'a' by uppercase 'A', except when preceded by a space
    static string ReplaceLowercaseA(string text)
    {
        char[] chars = text.ToCharArray();  // Convert the string to a character array
        for (int i = 0; i < chars.Length; i++)
        {
            // Check if the current character is 'a' and not preceded by a space
            if (chars[i] == 'a' && (i == 0 || chars[i - 1] != ' '))
            {
                chars[i] = 'A';  // Replace 'a' with 'A'
            }
        }
        return new string(chars);  // Convert the modified character array back to a string
    }

    // Method to extract the initials (first letter and those after a space)
    static string GetInitials(string text)
    {
        string initials = string.Empty;  // Initialize an empty string for initials

        // Loop through each character of the input text
        for (int i = 0; i < text.Length; i++)
        {
            if (i == 0 || text[i - 1] == ' ')  // If it's the first character or follows a space
            {
                initials += text[i];  // Add the character to the initials string
            }
        }
        return initials;  // Return the initials string
    }

    // Method to display odd-index letters in uppercase and even-index letters in lowercase
    static string OddEvenCase(string text)
    {
        char[] chars = text.ToCharArray();  // Convert the string to a character array
        for (int i = 0; i < chars.Length; i++)
        {
            if (i % 2 == 0)  // Even index (0, 2, 4, ...)
            {
                chars[i] = Char.ToLower(chars[i]);  // Make even-index letters lowercase
            }
            else  // Odd index (1, 3, 5, ...)
            {
                chars[i] = Char.ToUpper(chars[i]);  // Make odd-index letters uppercase
            }
        }
        return new string(chars);  // Convert the modified character array back to a string
    }
}