rank suffix script

var rank, suffix, srank;
rank = argument0;
srank = string(rank);

if (string_length(srank) == 2)
{
    if (rank < 21 && rank > 9)
    {
        suffix = "th";
    }
    else
    {
        switch (string_char_at(srank, string_length(srank)))
        {
            case "1": suffix = "st"; break;
            case "2": suffix = "nd"; break;
            case "3": suffix = "rd"; break;
            default: suffix = "th"; break;
        }
    }
}
else
{
    switch (string_char_at(srank, string_length(srank)))
    {
        case "1": suffix = "st"; break;
        case "2": suffix = "nd"; break;
        case "3": suffix = "rd"; break;
        default: suffix = "th"; break;
    }
}
return srank + suffix;