How to Toggle String Case in .NET

Algorithm by Robert R.:

protected string ToggleCaseByRobert(string s)
{
    var sb = new StringBuilder(s.Length);
    foreach (char c in s)
        sb.Append(char.IsUpper(c) ? char.ToLower(c) : char.ToUpper(c));
    return sb.ToString();
}

Algorithm by John S.:

protected string ToggleCaseByJohn(string s)
{
    StringBuilder mystring = new StringBuilder(s);
    for (int i = 0; i < mystring.Length; i++) {
        char c = mystring[i];
        mystring[i] = Char.IsLower(c) ? Char.ToUpper(c) : Char.ToLower(c);
    }
    return mystring.ToString();
}