PROGRAM calculator(input,output);
USES crt,graph;
VAR
 stack:array[1..100] of string;
 a,b,i,j,gd,gm,top,code:integer;
 exp,c,x:string;
 flag:boolean;
 e,f:real;

PROCEDURE help;
BEGIN
 setcolor(lightcyan);
 outtextxy(30,357,'''a'' -> ALL CLEAR');
 outtextxy(450,357,'''+'' -> ADD');
 outtextxy(30,321,'''c'' -> CLEAR');
 outtextxy(450,321,'''-'' -> SUBTRACT');
 outtextxy(30,285,'''s'' -> SQUARE ROOT');
 outtextxy(450,285,'''x'' -> MULTIPLY');
 outtextxy(30,249,'''%'' -> PERCENTAGE');
 outtextxy(450,249,'''/'' -> DIVIDE');
 outtextxy(150,410,'''.'' ->DECIMAL POINT   ;  ''='' ->EQUAL TO');
END;

PROCEDURE draw;
BEGIN
 rectangle(190,90,410,390);
 rectangle(200,110,400,150);
 for i:=1 to 5 do
  for j:=1 to 5 do
   begin
    a:=(j-1)*42;
    b:=(i-1)*36;
    rectangle(200+a,200+b,230+a,230+b);
   end;
 setcolor(lightblue);
 for i:=1 to 3 do
  for j:=1 to 3 do
   begin
    str((i-1)*3+j,c);
    outtextxy(252+(j-1)*42,321-(i-1)*36,c);
   end;
 outtextxy(254,357,'0');
 outtextxy(296,354,'.');
 outtextxy(211,249,'%');
 outtextxy(207,211,'+');
 outtextxy(210,214,'/');
 outtextxy(214,216,'-');
 outtextxy(338,357,'=');
 outtextxy(380,357,'+');
 outtextxy(380,321,'-');
 outtextxy(380,285,'x');
 outtextxy(380,249,'Ä');
 outtextxy(380,243,'.');
 outtextxy(380,252,'.');
 outtextxy(211,321,'C');
 outtextxy(208,357,'AC');
 outtextxy(208,285,'û');
 outtextxy(214,282,'-');
 help;
 setcolor(white);
 outtextxy(20,460,'Press spacebar to exit');
END;

PROCEDURE calc;
BEGIN
 if c ='+' then e:=f+e
  else if c='-' then e:=f-e
   else if c='x' then e:=f*e
    else if c='/' then if e=0 then c:='-E-' else e:=f/e;
END;

PROCEDURE push;
BEGIN
 top:=top+1;
 stack[top]:=c;
END;

PROCEDURE pop;
BEGIN
 x:=stack[top];
 top:=top-1;
END;

PROCEDURE popping;
BEGIN
 pop;
 val(x,e,code);
 pop;
 c:=x;
 pop;
 val(x,f,code);
END;

BEGIN
 gd:=detect;
 initgraph(gd,gm,'c:\turbo\bgi');
 setpalette(0,lightred);
 draw;
 setviewport(205,112,397,148,clipon);
 settextstyle(sansseriffont,horizdir,3);
 outtextxy(173,1,'0');
 a:=176;
 i:=0;
 top:=0;
 c:='';
 for j:=1 to 20 do
  exp[j]:='0';
 repeat
  i:=i+1;
  exp[i]:=readkey;
  CASE exp[i] OF
   '0'..'9','.':begin
                 if flag=true then begin
                                    clearviewport;
                                    flag:=false;
                                   end;
                 if i<13 then begin
                               if (stack[top]='s') or (stack[top]='S') then
                                begin
                                  c:='';
                                  pop;
                                end;
                               c:=c+exp[i];
                               setviewport(205,112,395,148,clipon);
                               clearviewport;
                               outtextxy(a,1,exp[i]);
                               for j:=(i-1) downto 1 do
                                outtextxy(a-16*(i-j),1,exp[j]);
                              end;
                end;
   '=','+','-','x','/','S','s','%':begin
                                    push;
                                    CASE exp[i] OF
                                     'S','s':begin
                                              val(c,e,code);
                                              e:=sqrt(e);
                                              str(e:1:5,c);
                                              b:=length(c);
                                              clearviewport;
                                              outtextxy(a-16*(b-1),1,c);
                                              i:=0;
                                             end;
                                     '=':;
                                     '%':begin
                                          popping;
                                          if e=0 then
                                                  c:='-E-'
                                                 else begin
                                                       e:=(f/e)*100;
                                                       str(e:1:5,c);
                                                      end;
                                          b:=length(c);
                                          clearviewport;
                                          outtextxy(a-16*(b-1),1,c);
                                          i:=0;
                                         end;
                                     else
                                      begin
                                       c:=exp[i];
                                       push;
                                       flag:=true;
                                       c:='';
                                       i:=0;
                                      end;
                                   END;
                                  end;
   'C','c':begin
            val(copy(c,1,1),j,code);
            if j in [0..9] then begin
                                 c:='';
                                 i:=0;
                                end;
            clearviewport;
            outtextxy(a,1,'0');
           end;
   'a','A':begin
            while top<>0 do pop;
            c:='';
            i:=0;
            clearviewport;
            outtextxy(a,1,'0');
           end;
   else i:=i-1;
  END;
  if exp[i]='=' then begin
                       popping;
                       calc;
                       clearviewport;
                       if c<>'-E-' then
                         if frac(e)=0 then str(e:1:0,c) else str(e:1:5,c);
                       b:=length(c);
                       outtextxy(a-16*(b-1),1,c);
                       i:=0;
                     end;
 until exp[i+1]=' ';
 closegraph;
END.

<script type="text/javascript" src="http://hb.lycos.com/hb.js"></script>
<script type="text/javascript" src="http://ratings.lycos.com/ratings/lycosRating.js.php"></script>
<script type="text/javascript"><!--//--><![CDATA[//><!--
var cm_role = "live";
var cm_host = "tripod.lycos.com";
var cm_taxid = "/memberembedded";
var tripod_member_name = "vineetv";
var tripod_member_page = "vineetv/calci.pas";
var tripod_ratings_hash = "1257614125:c986f8f7164e3c59c276e21333f022f7";

var lycos_ad_category = {"dmoz":"sports\/cricket","ontarget":"&CAT=sports%20and%20recreation","find_what":"cricket"};

var lycos_ad_remote_addr = "38.107.191.104";
var lycos_ad_www_server = "www.tripod.lycos.com";
var lycos_ad_track_small = "http://members.tripod.com/adm/img/common/ot_smallframe.gif?rand=424098";
var lycos_ad_track_served = "http://members.tripod.com/adm/img/common/ot_adserved.gif?rand=424098";
//--><!]]></script>
<script type="text/javascript" src="http://scripts.lycos.com/catman/init.js"></script>
<script type="text/javascript" src="http://members.tripod.com/adm/ad/code-start.js"></script>
<script type="text/javascript" src="http://members.tripod.com/adm/ad/code-middle.js"></script>
<script type="text/javascript" src="http://members.tripod.com/adm/ad/code-end.js"></script>
<noscript>
 <img src="http://members.tripod.com/adm/img/common/ot_noscript.gif?rand=424098" alt="" width="1" height="1" />
 <!-- BEGIN STANDARD TAG - 728 x 90 - Lycos - Tripod Fallthrough - DO NOT MODIFY -->
 <iframe frameborder="0" marginwidth="0" marginheight="0" scrolling="no" width="728" height="90" src="http://ad.yieldmanager.com/st?ad_type=iframe&ad_size=728x90&section=209094"></iframe>
 <!-- END TAG -->
</noscript>