Binary Search Help

[Qamar]

one of our assignments is to ask the user to enter in a last name to find from a text file, we have to take the text file and put it into an array... then call a function to do a binary search to find it... the code compiles fine, but when i call the function on line 19 it says the variable has no value...

Turing:

var lastname, firstname : array 1 .. 500 of string var fin : int var count := 0 open : fin, "sortedlist.txt", get loop     exit when eof (fin)     count += 1     get : fin, lastname (count), firstname (count)     put lastname (count), " ", firstname (count) end loop close : fin function bin_search (name : string) : int     var hi, lo, mid : int     hi := upper (lastname)     lo := lower (lastname)     mid := (hi + lo) div 2     var x : int := -1     if name > lastname (mid)  then          lo := mid + 1     elsif name < lastname (mid) then         hi := mid - 1     end if     if lo > hi then         result x     elsif name = lastname (mid) then         result mid     end if end bin_search var choice : string put "what name are you looking for ?" get choice choice := Str.Upper (choice) if bin_search (choice) = -1 then     put choice, " is not on the list" else     put choice, " is number ", bin_search (choice) end if

[Tony]

well, what are the values of all the variables used on that line?

Also, I'm really impressed by how your bin_search runs in O(1)

[Qamar]

on the line, name is passed by choice, so that should be the name that is entered and lastname (mid) is the name on the array. and i made the array global. i'm not seeing why either of the variables shouldn't have a value. and ... thank you ? haha are i'm not sure if your joking about it being a binary search or not ... this is what our teacher called it.

edit: ops.. ignore the

Turing:

put lastname (count), " ", firstname (count)

i just had that there to make sure that the file was going into the array.[/syntax]

[Qamar]

never mind... i got it to work... my mid wasn't being declared properly... so i had to figure out the actual max of the array... why wouldn't upper / lower work ?... because wouldn't it determine the beginning and the end of the array ?

here's my code...

Turing:

var lastname, firstname : array 1 .. 500 of string var fin : int var count := 0 open : fin, "sortedlist.txt", get loop     exit when eof (fin)     count += 1     get : fin, lastname (count), firstname (count) end loop function bin_search (name : string) : int     var hi, lo, mid : int     hi := count     lo := 1     var x : int := -1     loop         mid := (hi + lo) div 2         exit when lo > hi or name = lastname (mid)         if name > lastname (mid) then             lo := mid + 1         elsif name < lastname (mid) then             hi := mid - 1         end if             end loop     if lo > hi then         result x     end if     if name = lastname (mid) then         result mid     end if end bin_search var choice : string put "what name are you looking for ?" get choice choice := Str.Upper (choice) if bin_search (choice) = -1 then     put choice, " is not on the list" else     put choice, " is number ", bin_search (choice) end if close : fin