Binary Searching Listing Program

program BINARY_SEARCHING;
uses wincrt;
const nmax=20;

var
   data:array[1..nmax]of integer;
   i,j,k,atas,bawah,tengah,n,m,posisi,temp:integer;jawab:char;
   cari,pil:integer;ada:boolean;

procedure input;
begin
  gotoxy(25,2);write('Binary Searching '); writeln;
  gotoxy(25,3);write('______ _________ ');
  writeln;
  gotoxy(25,5);write('*****************');
  writeln;
  gotoxy(25,6);write('OMMY');
  writeln;
  gotoxy(25,7);write(' 04.04.111.00380 ');
  writeln;
  gotoxy(25,8);write('Tekn. Informatika');
  writeln;
  gotoxy(25,9);write('        A        ');
  writeln;
  gotoxy(25,10);write('*****************');
  writeln;
  writeln;
  write('enter your own data = ');readln(n);
  writeln('input ', n ,' number!');
  for j:=1 to n do
  readln(data[j])
end;

procedure sort;
begin
  for i:=2 to n do
  for j:=n downto i do
  if data[j]>data[j-i] then
 begin
  temp:=data[j];
  data[j]:=data[j-1];
  data[j-1]:=temp;
 end;
end;

procedure biner ;
begin;
  ada:=false;
  atas:=n;down:=1;

  while atas>=down do
 begin
  center:=(up+down)div 2;

  if find
   atas:=tengah-1

  else if find>data[center] then
   atas:=center+1
                    
  else
   ada:=true;
   down:=up+1;
 end;
end;


begin
  input;
  urut;
  write('enter code=');readln(find);
  biner;
  if exist=true then

  writeln('data available')
  else
  writeln('data empty');
end.