{$I-}
program ChkZero;
type byte = -128..127;
var fn : string[39];
    f: file;
    ior,blk,nblk,i,start,finish: integer;
    ans: char;
    Stop : boolean;
    twoblocks : array[0..1024] of byte;
begin
  writeln('CHKZERO - Check text file for embedded 0');
  write('Enter file name : '); readln(fn);
  reset(f,fn); ior := ioresult;
  if ior <>0 then
     begin
     writeln('IOresult = ',ior:1);
     exit(ChkZero);
     end;
  blk := 2; Stop := FALSE;
  repeat
     writeln('Reading 2 blocks starting at block ',blk:1);
     nblk := blockread(f,twoblocks,2,blk);
     ior := ioresult;
     if (nblk = 2) and (ior = 0) then
        begin
        i := 0;
        while ( (i<1024) and (twoblocks[i] <> 0) ) do i := i+1;
        start := i;
        while ( (i<1024) and (twoblocks[i] = 0) ) do i := i+1;
        finish := i;
        if (i < 1024) then
           begin
           writeln(chr(7),'Found a block with a zero(s) embedded.');
           write('zero start block number = ',blk + (start div 512) );
           writeln('  start byte = ',start:1);
           write('zero end block number = ',blk + (finish div 512) );
           writeln('  end byte = ',finish:1);
           ans := 'N';
           write('Continue? [Y/N] N',chr(8)); read(ans); writeln;
           Stop := NOT( (ans = 'Y') or (ans='y') );
           end;
        blk := blk + 2;
        end
     else
        begin
        writeln('Blockread failed...  IOresult = ',ior:1);
        writeln('starting block = ',blk:1,'  number of blocks read = ',nblk:1);
        Stop := TRUE;
        end;
     until (Stop);
  close(f);
end.