Pascal help please: loop through files in directory

program muuuu;
uses
  crt;
var
  i : integer;
  yesno : boolean;
  janej : char;

  procedure search;
  const
    format = '.txt';
  var
    a,b,c : array [0..255] of char;
    filnamn : string;
    antal, x : integer;

     function exists(filnamn:string):boolean;
     var
      fil : text;
     begin
       exists := false;
       assign(fil,filnamn);
       {$I-}reset(fil);{$I+}
      if IOResult = 0 then begin
        close(fil);
        writeln(filnamn);
        exists := true;
      end;
     end;

  begin
    antal := 0;
    for x := 1 to 255 do begin
      a[x] := chr(x);
      filnamn := a[x]+format;
      if exists(filnamn) then
        inc(antal);
    end;
    writeln('There are ',antal,' files in this folder.');
  end;

begin
  clrscr;
  writeln('Do you want to scan folder?');
  readln(janej);
  if janej in ['Y','y'] then begin
    clrscr;
    writeln('The files are as follows:');
    search;
  end
  else
    halt;
  readln();
end.

  procedure search;
  const
    format = '.txt';
  var
    a,b,c : array [0..255] of char;
    filnamn : string;
    antal, x : integer;

 -- snip --

  begin
    antal := 0;
    for x := 1 to 255 do begin
      a[x] := chr(x);
      filnamn := a[x]+format;
      if exists(filnamn) then
        inc(antal);
    end;
    writeln('There are ',antal,' files in this folder.');
  end;