Curl with for loop error - php

Question

Script is running without implementing for loop, but when I place a for loop it fails.
Working script:
$dob=new DateTime('28-12-83');
$regno='1984';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'http://domain.com/login.php');
curl_setopt ($ch, CURLOPT_POST, 1);
curl_setopt ($ch, CURLOPT_POSTFIELDS, 'op=&sub=3&txtregno='.$regno.'&txtrollno=&txtpass=&txtdob='. $dob->format('d-m-y'));
curl_setopt ($ch, CURLOPT_COOKIEJAR, 'cookie.txt');
curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
$store = curl_exec ($ch);
curl_setopt($ch, CURLOPT_URL, 'http://domain.com/results.php');
curl_setopt ($ch, CURLOPT_COOKIEJAR, 'cookie.txt');
$fp = fopen('mm.htm', 'w');
curl_setopt ($ch, CURLOPT_FILE, $fp);
$store = curl_exec ($ch);
fclose($fp);
curl_close ($ch);
Above script is running good and generate a mm.htm file with output.
Incorrect script after for loop
$dob=new DateTime('27-12-83');
$regno='1984';
for($i=1; $i<=3; $i++)
{
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'domain.com/login.php');
curl_setopt ($ch, CURLOPT_POST, 1);
curl_setopt ($ch, CURLOPT_POSTFIELDS, 'op=&sub=3&txtregno='.$regno.'&txtrollno=&txtpass=&txtdob='. $dob->format('d-m-y'));
curl_setopt ($ch, CURLOPT_COOKIEJAR, 'cookie.txt');
curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
$store = curl_exec ($ch);
curl_setopt($ch, CURLOPT_URL, 'domain.com/results.php');
curl_setopt ($ch, CURLOPT_COOKIEJAR, 'cookie.txt');
$fp = fopen($regno."_".$i.'.htm', 'w');
curl_setopt ($ch, CURLOPT_FILE, $fp);
$store = curl_exec ($ch);
fclose($fp);
$dob->modify('+1 day');
set_time_limit(0);
curl_close ($ch);
}
Above script generates 3 htm files but without any output. It means this script fails somewhere, but I failed to trace the problem.

Answer 1

If you want to store the received contents in the file you specify with CURLOPT_FILE, surely you shouldn't also use CURLOPT_RETURNTRANSFER to ask for it to get returned? Or perhaps I should ask you why you do that?