Creating a comma delimited string from an array came up yesterday, here is a couple of methods, one from our junior developer and one that I did.  I entitled mine old school, because of the C coding that shaped my programming.

static internal String Junior(String[] list)
{
    String output = String.Empty;

    foreach (String item in list)
    {
        output += item + ",";
    }

    output.TrimEnd(',');

    return (output);
}

static internal String OldSchool(String[] list)
{
    StringBuilder output = new StringBuilder();

    foreach (String item in list)
    {
        if (String.IsNullOrEmpty(item))
            continue;

        if (output.Length > 0)
            output.Append(",");

        output.Append(item);
    }

    return (output.ToString());
}

Which one do you like?

{6230289B-5BEE-409e-932A-2F01FA407A92}