Задача: ROT13

ROT13.cs

using System;
using System.Text;
					
public class Program
{
	private static string ROT13(string str)
	{
		StringBuilder result = new StringBuilder();
		for (int i = 0; i < str.Length; i++)
		{
			int code = (int)str[i];
			if (code >= 'a' && code <= 'm' || code >= 'A' && code <= 'M')
			{
				code += 13;
			}
			else if (code >= 'n' && code <= 'z' || code >= 'N' && code <= 'Z')
			{
				code -= 13;
			}

			result.Append((char)code);
		}
		return result.ToString();
	}
	
	private static void Test_ROT13(string str)
	{
		Console.WriteLine(string.Format("Input string = {0}", str));
		string codedMsg = ROT13(str);
		Console.WriteLine(string.Format("Coded string = {0}", codedMsg));

		string decodedMsg = ROT13(codedMsg); // should be equal to the original message
		Console.WriteLine(string.Format("Decoded string = {0}", decodedMsg));
		Console.WriteLine(string.Format("Is valid = {0}\n\n", str.Equals(decodedMsg)));
	}
	
	public static void Main()
	{
		Console.WriteLine("UniLecs");
		
		Test_ROT13("Subscribe to UniLecs!");
		Test_ROT13("Make Russia Great Again!");
	}
}