Pascal LinkedList example

program LinkedLists;

type

  NodePointerType = ^NodeType;

  NodeType = record
    Name: string[30];
    NextPointer: NodePointerType;
  end;

var
  Head, Tail, Current: NodePointerType;

  procedure Add(Name: string);
    begin
       new(Current);
       Current^.Name := Name;
       Current^.NextPointer := nil;
       if Head = nil then
          Head := Current
       else
          Tail^.NextPointer := Current;
       Tail := Current;
    end;

  procedure ViewAll;
    var
      n: word;

    begin
       Current := Head;
       n := 0;
       while Current <> nil do
          begin
             writeln(n, ': ', Current^.Name);
             Current := Current^.NextPointer;
             n := n + 1;
          end;
      writeln()
    end;

  procedure DeleteAll;
    begin
       Current := Head;
       while Current <> nil do
          begin
             Current := Current^.NextPointer;
             dispose(Head);
             Head := Current;
          end;
    end;

  procedure ViewByIndex(index: word);
    begin
      var
        n: word;

        Current := Head;
        n := 0;
        while Current <> nil do
          begin
            if index = n then
              begin
                writeln(Current^.Name);
                break;
              end;
            n := n + 1;
            Current := Current^.NextPointer;
          end;
    end;

  procedure DeleteByIndex(index: word);
    var
      PreviousNode: NodePointerType;
      n: word;

    begin
        Current := Head;
        if index = 0 then
          begin
            Current := Current^.NextPointer;
            dispose(Head);
            Head := Current;
            Exit;
          end;

        n := 0;
        while Current <> nil do
          begin
            if index = n then
              begin
                PreviousNode^.NextPointer := Current^.NextPointer;
                dispose(Current);
                Exit;
              end;
            n := n + 1;
            PreviousNode := Current;
            Current := Current^.NextPointer;
          end;
    end;

  procedure AddByIndex(index: word; Name: string);
    var
      NextNode, PreviousNode: NodePointerType;
      n: word;

    begin
        new(Current);
        Current^.Name := Name;
        if index = 0 then
          begin
            Current^.NextPointer := Head;
            Head := Current;
            Exit;
          end;

        n := 0;
        NextNode := Head;
        while NextNode <> nil do
          begin
            if index = n then
              begin
                Current^.NextPointer := PreviousNode^.NextPointer;
                PreviousNode^.NextPointer := Current;
                Exit;
              end;
            n := n + 1;
            PreviousNode := NextNode;
            NextNode := NextNode^.NextPointer;
          end;
        if NextNode = nil then
          Add(Name);
    end;

  procedure ReplaceByIndexSlow(index: word; Name: string);
    begin
      DeleteByIndex(index);
      AddByIndex(index, Name);
    end;

  procedure ReplaceByIndexFast(index: word; Name: string);
    //under construction
    {var
      NextNode, PreviousNode: NodePointerType;
      n: word;

    begin
        if index = 0 then
          begin
            if Head = nil then
              Add(Name)
            else

            Current^.NextPointer := Head;
            Head := Current;
            Exit;
          end;

        n := 0;
        NextNode := Head;
        while NextNode <> nil do
          begin
            if index = n then
              begin
                Current^.NextPointer := PreviousNode^.NextPointer;
                PreviousNode^.NextPointer := Current;
                Exit;
              end;
            n := n + 1;
            PreviousNode := NextNode;
            NextNode := NextNode^.NextPointer;
          end;
        if NextNode = nil then
          Add(Name);}
    end;

begin
  Head := nil;
  Add('Kolya');
  Add('Dasha');
  Add('Klim');
  Add('Longnamedmen');
  Add('Sh');

  //ViewByIndex(2);

  ViewAll;

  ReplaceByIndexSlow(2, 'Replaced');
  //AddByIndex(5, 'Addedbyindex');

  //DeleteByIndex(0);
  //DeleteByIndex(4);
  //DeleteByIndex(2);

  ViewAll;

  //DeleteAll;
end.