This document discusses the Pascal programming language and the stack data structure. It defines a stack as a last-in, first-out abstract structure containing elements with the same data type and references to the next element. Procedures for pushing and popping elements onto and from the stack are presented using a linked list implementation with a record containing a character and next pointer. The code sample demonstrates pushing all characters of a string onto the stack and then popping and writing them out in reverse order.

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. So the STACK is:
An Abstract Structure based on the principle (LIFO) “Last in
First out”.
Thinking Of MAKDOOS right now :P :P :P :P .

5. It has two elements:
1. TheVariable(s) with Data type(s) “the same with all the
stacks elements”.
2. The References which refers to the next element in the
Stack (it refers to the element underneath).
This Reference has the value of (nil) in the Bottom of the
Stack.
3. The Stack has the (Top) which refers to the top element in
the Stack ….This is the reference we have keep :D.

6. Program test1;
Type
n_stack = ^stack;
stack = record
c : char;
next : n_stack;
end;
Now let’s meet with PUSH & POP
as Procedures :P

7. Procedure Push (var top: n_stack ; ch: char)
Var
temp : n_stack;
Begin
new(temp);
temp^.c := ch;
temp^.next := top;
top := temp;
End;

8. Procedure Pop (var top: n_stack ;var ch: char)
Var
temp : n_stack;
Begin
ch := top^.c;
temp := top;
top := top^.next;
dispose (temp);
End;

9. Var
s : string[10]; ch:char;
top : n_stack;
Begin
top := nil;
read(s);
for i:=1 to 10 do
Push(top,S[i]);
while (top <> nil) do
begin
Pop(top,ch); write(ch);
end;
End.