Pascal Programming Language Omar ElSabek & Fayez G hazzawi IT Engineering 3 th year – UNKNOWN Department programming II
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Pascal Programming Language
Omar ElSabek & Fayez GhazzawiIT Engineering3th year – UNKNOWN Department
programming II
Sets
Record
Files (Text & Binary)
Pointers
Linked Lists
Unit
Course Index :
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 ListThis 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 ListThis Reference has the value of (nil) in the first element in the Linked List.
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
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
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
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;
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
else
begin
S^.prev^.next := temp;
temp^.prev := S^.prev;
S^.prev := temp;
end;
end;
End;
It has three cases:
1. Delete the first element
2. Delete the last element
3. Delete any other element
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
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
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;
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