Search Queue

I am attempting to write a program that emulates First In First Out Page Replacement.

Ultimately the program will read files of random integers, generated from a seperate program.  Currently I am entering integers manually for testing purposes.

I need to to include a search procedure that will check if the integer has already been added.  If the integer is found a "Page found : No change" message will be displayed.  If the item has not already been added the Replace procedure will be intitiated.

I've got myself in a muddle with the Search procedure and would be glad of help.

WTA

LRH

{Unit to simulate First In First Out Page Replacement }

unit FIFOCls4;
interface
uses crt;
type TQptr = ^QRec; {define Q record structure}
QRec = record
     element: integer;
     next: TQptr;
end;

QType = object {define Q structure and methods}
      head, tail : TQptr;
      Qsize, numInQ, Counter: integer;
 
      procedure Init(iMax : integer);
      procedure Add(nData : integer);
      procedure Retrieve;
      procedure DisplayQ;
      procedure Search (item : integer);
      procedure Replace(jData:integer);
      {procedure Output;}
end;

implementation

{
Method : Used to initialise Q
precondition : Q is defined
postcondition: maxsize of Q, num in Q and head & tail properties and counter set
}

procedure QType.Init(iMax : integer); {Set maximum Q size}
begin
     Qsize := iMax;
     NumInQ := 0;
     head := nil;
     tail := nil;
     Counter := 0;
end;

{
Method : Used to ADD data to Q
precondition : Q is initialised, and input data is an integer
postcondition: data added to Q and tail referenced to new element
}

procedure QType.Add(nData : integer);
var i : integer;
newElem : TQptr;
begin
   new(newElem);
   newElem^.element := nData; {set data to new element}
   newElem^.next := nil; {as element will be tail then set to nil}
      if tail <> nil then tail^.next := newElem; {point current tail of Q to new element}
      tail := newElem; {set tail to new element}
         if head = nil then head := tail; {set head to tail if nohing in Q}
         Inc(numInQ);
end;

{
Method : Used to RETRIEVE data from Q
precondition : Q has integer data present
postcondition: head of Q is removed and head moved to next item
}

procedure QType.Retrieve;
var i : integer;
tempQ : TQptr;
begin
   tempQ := head;
   head := head^.next; {point head of Q to next element}
   dispose(tempQ); {release memory}
   Dec(numInQ); {reduce number in Q}
      if numInq = 0 then tail := nil; {reset tail if no data in Q}
   Inc(Counter);
end;

{
Method : Used to DISPLAY data from Q
precondition : Q has integer data present
postcondition: data displayed from head onwards.
}

PROCEDURE QType.DisplayQ;
var tempQ : TQptr;
begin
   writeln('Items in Q ...');
   tempQ:= head;
      while tempQ <> nil do
      begin
      writeln(tempQ^.element);
      tempQ := tempQ^.next;
      end
end;

{
Method : Used to REPLACE data in Q
precondition : the data is not in Q
postcondition: head of Q is removed and
             the new data added to Q
}

procedure QType.Replace(jData:integer);
begin
   if NumInQ < Qsize then
   begin
   QType.Add(jData);
   writeln('Not Full Int Added : ',jData);
   writeln ('No items in Q : ', NumInQ);
   DisplayQ;
   end
      else
      begin
      QType.Retrieve;
      writeln('Q Full Int Removed');
      writeln ('No items in Q : ', NumInQ);
      QType.Add(jData);
      writeln('New Int Added : ',jData);
      writeln ('No items in Q : ', NumInQ);
      DisplayQ;
      end;
writeln('Fault Count = ', counter);
writeln;
end;

{
Method : Used to SEARCH for data
precondition : Q must be initialised and item to search for must be an integer
postcondition: if item found, confirmation message is displayed
               if item not found, Replace procedure intiated
}

Procedure QType.Search(item : integer);
var i, jData : integer;
currPos : TQptr;
begin
   currPos := head;
      if head <> nil then
      begin
         while currPos <> nil do
         begin
            if item = currPos^.element then
            begin
            Search := currPos;
            Exit;
            end;
         currPos := currPos^.next;
         end;
      end;
   Search := nil;  

{If Search <> nil then writeln ('Page found : No change');}
{If Search = nil then Replace(jData);}
     
end;