using System;

​

public class Exercise16 {

    public static void Main(string[] args)

    {

        Console.WriteLine(SwapFirstAndLastLettersExplained("w3resource"));

        Console.WriteLine(SwapFirstAndLastLettersExplained("Python"));

        Console.WriteLine(SwapFirstAndLastLettersExplained("x"));

    }

    public static string SwapFirstAndLastLettersExplained(string inputString)

    {

        if(inputString.Length == 1) // One letter means no swapping required

            return inputString;

​

        // We can get bits of a string with SubString

        // So "Hello World".Substring(3,5) gives "lo Wo", because it's the letter at position 3

        // and the next letters until we have 5 all together.

        // Note that strings are 0 indexed, so letter at position 3 is the fourth letter, like so:

        /*

             0 1 2 3 4 5 6 7 8 9 10

             H e l l o   W o r l d

        */

        // Get the first letter, then keep including letters until our string is length 1.

        var firstLetter = inputString.Substring(0, 1); 

        // Get the letter at position equal to the length of the string - 1

        // (remember this will always be the last letter becasue our string is zero indexed

        // so a string with length 6 will have the last letter in position 5 (or 6 - 1):

        //  0 1 2 3 4 5 <- position 5

        //  S T R I N G <- length 6

        var lastLetter = inputString.Substring(inputString.Length - 1, 1);

        // The remaining string, then, is start at position 1 (the second letter)

        // and continue going until the string is the length of the initial string

        // but with two letters missing.

        var remaining = inputString.Substring(1, inputString.Length - 2);

        // Concat them all together:

        return lastLetter + remaining + firstLetter;

        // Note, you should actually use this:

        // return string.Concat(lastLetter, remaining, firstLetter);

        // rather than +ing the string together, but whatever.

    }

}