Bubble Sort logical error VB.NET -

this program suppose sort records(in arysort) in ascending order last name(index 1 in arytemp , arytemp2) , place result in list box on old, preloaded, unsorted records.

it sorts them strangely, have click multiple times ascending button actual sort result suppose clicking button once.

why doesn't sort items single mouse click?

the source:

public class form1     dim file_name string = "students.txt"     dim numberofrecords integer 'total number of records     private sub form1_load(byval sender system.object, byval e system.eventargs) handles mybase.load         if system.io.file.exists(file_name) = true             dim objreader new system.io.streamreader(file_name)             while objreader.peek() <> -1                 lstbox.items.add(objreader.readline)                 numberofrecords += 1             loop             objreader.close()         end if     end sub      private sub btnascending_click(byval sender system.object, byval e system.eventargs) handles btnascending.click         'load students array         dim arysort(numberofrecords - 1) string         dim arytemp() string 'holds first record's last name         dim arytemp2() string 'holds second record's last name         = 0 numberofrecords - 1             arysort(i) = lstbox.items(i)         next         dim temp string 'holds temporary record         dim k integer         = 0 arysort.length - 2             arytemp = split(arysort(i), " ")             k = + 1 arysort.length - 1                 arytemp2 = split(arysort(k), " ")                 if arytemp(1) < arytemp2(1)                     temp = arysort(k)                     arysort(k) = arysort(i)                     arysort(i) = temp                 end if             next         next         lstbox.items.clear()         numberofrecords = 0         = 0 arysort.length - 1             lstbox.items.add(arysort(i))             numberofrecords += 1         next     end sub end class 

if need sort list (as in comment), don't implement own sort mechanism use 1 of .net:

' define how want compare items ' function comparebylastname(byval item1 string, byval item2 string) integer     return string.compare(item1.split(" ")(1), item2.split(" ")(1)) end function  private sub btnascending_click(byval sender system.object, byval e system.eventargs) handles btnascending.click     ' load students array '     dim arysort(numberofrecords - 1) string     = 0 numberofrecords - 1         arysort(i) = lstbox.items(i)     next      ' use built-in .net magic '     array.sort(arysort, addressof comparebylastname)      ' write values list box '     lstbox.items.clear()     numberofrecords = 0     = 0 arysort.length - 1         lstbox.items.add(arysort(i))         numberofrecords += 1     next end sub 

this uses built-in quicksort algorithm of .net class library. here's documentation of method using: array.sort(t(), comparison(of t)).