This document discusses the Pascal programming language and some of its key features including sets, records, files, pointers, linked lists, and units. It then focuses on describing the structure of a doubly linked list in Pascal which includes the data type, references to the next and previous elements, and examples of inserting and deleting elements from the list. Procedures are provided for inserting elements into the list in different locations and deleting elements from the start, end, or middle of the list.

1. Pascal Programming Language
Omar ElSabek & Fayez Ghazzawi
IT Engineering
3th year – UNKNOWN Department
programming II

2. Sets
Record
Files (Text & Binary)
Pointers
Linked Lists
Unit
Course Index :

4. It has three elements:
1. The Variable(s) with Data type(s) “the same with all the Linked
List elements”.
2. The References which refers to the next element in the Linked
List
This Reference has the value of (nil) in the last element in the
Linked List.
3. The References which refers to the previous element in the
Linked List
This Reference has the value of (nil) in the first element in the
Linked List.

5. Program test1;
Type
D_P = ^D_R;
D_R = record
num : integer;
next,prev : D_P;
end;
Now let’s meet with some procedures
which are used in DLL

6. It has three cases:
1. Insert an element in the first of DLL
2. Insert an element in the last of DLL
3. Insert an element anywhere else

7. Procedure Insert (var L_S,L_E: D_P; numb: integer)
Var
S,temp : D_P; located : boolean
Begin
new(temp);
temp^.num := numb;
temp^.next := nil;
temp^.prev := nil;
if (L_S = nil) then
begin
L_S := temp; L_E := temp;
end

8. else
begin
S := L_S; located := false;
while (S <> nil) and (not located) do
begin
if (S^.num < numb) then
S := S^.next;
else
located := true;
end;
temp^.next := S;

9. if (L_S = S) then
begin
L_S^.prev := temp;
L_S := temp;
end
else if (S = nil) then
begin
L_E^.next := temp;
temp^.prev := L_E;
L_E := temp;
end

10. else
begin
S^.prev^.next := temp;
temp^.prev := S^.prev;
S^.prev := temp;
end;
end;
End;

11. It has three cases:
1. Delete the first element
2. Delete the last element
3. Delete any other element

12. Procedure Delete(var L_S,L_E: D_P; numb: integer;
flag: char)
Var
S,temp : D_P;
Begin
if (L_S = nil) then flag := ‘0’;
if (numb = L_S^.num) then
begin
flag := ‘1’;
temp := L_S;
L_S := L_S^.next;
L_S^.prev := nil;
dispose(temp);
end

13. else if (numb = L_E^.num) then
begin
flag := ‘1’;
temp := L_E;
L_E := L_E^.prev;
L_E^.next := nil;
dispose(temp);
end

14. else
begin
S := L_S;
while (S <> nil) and (S^.num <> numb) do
S := S^.next
if (S = nil) then flag := ‘2’
else
begin
flag := ‘1’;
S^.next^.prev := S^.prev;
S^.prev^.next := S^.next;
dispose(S);
end;
end;
End;