Use recursion in the solution.

I would really appreciate if you can help me to find a better way to do it.

```
public class AppendCharacterAfterEachCharacterInString
{
    int index =0;
    StringBuilder outputString = new StringBuilder();

    public string AppendInputCharacterAfterEachCharacterInString(string sInputString, string inputRepeatCharacter)
    {            
        if (string.IsNullOrEmpty(sInputString))
        {
            Console.WriteLine("Empty string !");
        }
        else
        {
            BuildNewString(sInputString, inputRepeatCharacter);
        }

        return outputString.ToString();
    }

    private void BuildNewString(string inputString, string repeatCharacter)
    {
        if (index < inputString.Length)
        { 
            outputString.Append(inputString[index]);

            if(!(inputString[index].ToString().Trim() == string.Empty) && !(index + 1 == inputString.Length))
              outputString.Append(repeatCharacter);                  

            index++;
            BuildNewString(inputString, repeatCharacter);  
        }

    }

```