Given a string, return a string where every character in the original is doubled

For example, given the string "xyz", return the string "xxyyzz".

I was given this as a part of a test. I would really appreciate if you can help me to find a better way of doing it.

I came up with two methods to do the same thing but one was an extension method.

I have a couple more questions which I will post in separate posts.

public class RepeatCharactersInString
{               
    public string RepeatAString(string sInputString, int repeatCount)
    {

        StringBuilder sOutputString = new StringBuilder();
        if (string.IsNullOrEmpty(sInputString))
        {
            Console.WriteLine("Empty string !");
        }
        else
        {
            foreach (char c in sInputString)
            {
                sOutputString.Append(new String(c, repeatCount));
            }
        }

        return sOutputString.ToString();
    }

}

// Method 2 Using extension methods
public static class RepeatCharactersInStingExtensions
{

    public static string RepeatAllCharactersInThisString(this string sInputString, int repeatCount)
    {
        StringBuilder sOutputString = new StringBuilder();
        if (string.IsNullOrEmpty(sInputString))
        {
            Console.WriteLine("Empty string !");
        }
        else
        {
            foreach (char c in sInputString)
            {
                sOutputString.Append(new String(c, repeatCount));
            }
        }

        return sOutputString.ToString();
    }
}

No reason to write anything when string is empty.

public string RepeatAString(string sInputString, int repeatCount)
{
    StringBuilder sOutputString = new StringBuilder();

    foreach (char c in sInputString)
        sOutputString.Append(new String(c, repeatCount));

    return sOutputString.ToString();
}

I think your solution is the best. Obviously you can use LINQ if you want but IMO it doesn't bring anything to table.

public string RepeatAString(string input, int count)
{
    return String.Concat(input.Select(c => new String(c, count)));

}

StackExchange Code Review Q#51354, answer score: 3