Array used in listboxes?

[AceInfinity]

What do you mean "an array with 5 rows 3 columns"? An array is not a DataTable, although to visualize multi-dimensional arrays, it may be easier to picture it that way. I don't get what you're trying to do. Why don't you just do this if you want to add "A" to "E" in one ListBox and "1" to "3" in the other:

listBox1.Items.AddRange("ABCDEFG".Select(c => c.ToString()).ToArray());
listBox2.Items.AddRange(Enumerable.Range(1, 3).Select(i => i.ToString()).ToArray());

If you're meaning to add "A1", "A2", "A3", "B1", "B2", etc... to one Listbox, and "1A", "2A", 3A", ect... to the other Listbox. Then:

string s = "ABCDEFG";
string nums = "123";
 
var x1 = (from char c in s
          from char n in nums
          select string.Format("{0}{1}", c, n)).ToArray();
 
var x2 = (from char c in s
          from char n in nums
          select string.Format("{0}{1}", n, c)).ToArray();
 
listBox1.Items.AddRange(x1);
listBox2.Items.AddRange(x2);