Using the static String.Join method is a quick way to get a comma-delimited string. (I used to always run the array through a foreach loop tacking on a comma, and then removing the last comma outside the foreach loop--a bit messy). This code shows you how to take an array and convert it into a string delimited by commas in one nline. Of course, you can delimit your string with any character you want.
string[] ids = {"2343","2344","2345"};
string idString = String.Join(",",ids);
Response.Write(idString);
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