CODEWITHSUNDEEP
listdelphilazarus
s-f
s-f

Reputation: 11

Single linked list - delphi

I am starting to learn programming.

I have to do (HW) program where I can add in example name and surname, add it to single linked list and than display this single linke list.

I tried to do it, program is compiling and it is even working. I can add data and it is displayed. But I propably dont understan something and make mistake. I am adding first person, it is displayed, than I am adding second person, it is also displayed but the first person data is override by the second person I added. So I have two the same records. Listbox is only showing data from the single linked list so I suppose there is no problem. Each pointer should point different data so why each record is the same as the last one I added?

Here is my code:

    type
  wskaznik = ^Lista;

  Lista = record
    lp : string;
    dane : string;
    wsk : wskaznik;
  end;

var
  Form1 : TForm1;
  First, current : wskaznik;
  tekst : string;
  liczba : string;
  i, k : integer;


implementation

{$R *.lfm}

{ TForm1 }

procedure AddToList(dane : string; lp : string; var current : wskaznik);
var
  prev, Next : wskaznik;
begin
  if current <> nil then
  begin
    prev := current;
    Next := current^.wsk;
  end
  else
  begin
    prev := nil;
    Next := nil;
  end;

  new(current);
  current^.dane := dane;
  current^.lp := lp;
  current^.wsk := Next;
  if prev <> nil then
    prev^.wsk := current;
end;


procedure GetAddr(dane : string; var First, current : wskaznik);
var
  Next : wskaznik;
begin
  if First <> nil then
  begin
    Next := First;
    repeat
      if Next^.wsk <> nil then
        Next := Next^.wsk
    until (Next^.wsk = nil) or (Next^.dane = dane);
    current := Next;
  end;
end;


procedure GetNum(n : integer; var First, current : wskaznik);
var
  Next : wskaznik;
begin
  if First <> nil then
    if n = 1 then
      current := First
    else
    if (n = 2) and (First^.wsk = nil) then
      n := 0
    else
    begin
      Next := First;
      i := 1;
      repeat
        Inc(i);
        if Next^.wsk <> nil then
          Next := Next^.wsk
      until (i = n) or (Next^.wsk = nil);
      if (Next^.wsk = nil) and (i < n) then
        n := 0
      else
        current := Next;
    end;
end;



procedure List;
var
  l : integer;
begin
  form1.listbox1.Clear;
  form1.listbox2.Clear;
  for l := 1 to i do
  begin
    Getnum(l, First, current);
    if l > 1 then
      form1.listbox1.items.add(current^.dane);
    form1.listbox2.items.add(current^.lp);
  end;
end;


procedure findLess(dane : string; lp : string; var First, current : wskaznik);
var
  tmp, Next : wskaznik;
begin
  if First <> nil then
  begin
    Next := First;
    repeat
      if (Next^.wsk <> nil) then
      begin
        tmp := Next;
        Next := Next^.wsk;
      end;
    until (Next^.wsk = nil) or (Next^.dane > dane);
    if Next^.dane > dane then
      current := tmp
    else
      current := Next;
    if Next^.lp > lp then
      current := tmp
    else
      current := Next;
  end;
end;

procedure TForm1.Button1Click(Sender : TObject);
begin
  Inc(i);
  findLess(edit1.Text, edit2.Text, First, current);
  addtolist(edit1.Text, edit2.Text, current);
  label3.Caption := 'Elementów: ' + IntToStr(i - 1);
  //edit1.SetFocus;
  list;
end;






end.

Upvotes: 1

Views: 882

Answers (1)

Tom Brunberg
Tom Brunberg

Reputation: 21045

You never assign anything to First (assuming Firstis to be the beginning of the list). The first time you call AddToList you should assign Current to First

Upvotes: 2

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