program lol;
uses crt;
label metka1, metka2;
type Pprice=record
		   Pname:string[20];
		   Pvalue:real;
		   end;
var price:file of Pprice;
	  p:pprice;
	  i,n,z,x:integer;
procedure vivod;
begin
  reset(price);
   while not eof(price) do
	begin
	  read(price,p);
	  write(p.pname:10);
	  writeln(p.pvalue:10:2);
	  writeln;
	end;
	close(price);
end;

begin
clrscr;
  begin  {' otkritie '}
	assign(price,'C:\price.dat');
	write('noviy file - 0, redakt - 1  ');
	readln(i);
	if i=0 then rewrite(price) else reset(price);
  end;

	begin  {' dobavlenie '}
	write('dobavit? da - 1, net - 0  ');
	readln(n);
	if n=1 then
	begin
	  metka1:
	  seek(price,filesize(price));
	  write('vvedite na3vanie tovara  ');
	  read(p.pname);
	  write('vvedite na3vanie ceni  ');
	  read(p.pvalue); 
	  write(price,p);
	  write('dobavit? da - 1, net - 0  ');
	  readln(n);
	  if n=1 then goto metka1;
	end;
  close(price);
  end;

	vivod;

	begin  {' i3menenie '}
  reset(price);
	metka2:
	write('vvedite nomer stroki dlia i3meneniya  ');
	readln(i);
	seek(price,i-1);
	write('vvedite na3vanie tovara  ');
	read(p.pname);
	write('vvedite na3vanie ceni  ');
	read(p.pvalue);
	write(price,p);
	write('eshe redaktirovat? da - 1, net - 0  ');
	readln(n);
	if n=1 then goto metka2;
  close(price);
  end;

	vivod;

	begin  {' ydalenie '}
	write('vvedite nomer stroki dlia ydaleniya  ');
	readln(i);
	 ??? 

	end;

readln;
end.

const
  old_name = 'old.dat';
  new_name = 'new.dat';

...
{ здесь - создаешь новый файл new_file }
...
while not eof(old_file) do begin
  read(old_file, r); { ичтаем запись }
  if { какое-то условие, при выполнении которого запись НУЖНО переносить }
  then write(new_file, r);
end;

close(new_file); close(old_file);
erase(old_file);
rename(new_file, old_name);

  if filepos(old_file) <> 3 
  then write(new_file, r);

var
  price:file of Pprice;
  newprice:file of Pprice;
...
  rename(newprice,price);