我想用for循环和指针写一个C语言代码，输入一个数据后，能够计算出crc校验码并输出为一个二进制字符串，并写出代码注释

以下是一个简单的火车头采集器，每次采集时会随机更换User-Agent。

<?php
// 设置采集目标URL
$url = "http://www.example.com/";

// 设置User-Agent列表
$userAgents = array(
    "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36",
    "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36",
    "Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko",
    "Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11.0) like Gecko",
    "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:54.0) Gecko/20100101 Firefox/54.0",
    "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0",
);

// 随机选择一个User-Agent
$userAgent = $userAgents[array_rand($userAgents)];

// 设置HTTP请求头部信息
$headers = array(
    "User-Agent: " . $userAgent,
    "Accept-Language: en-US,en;q=0.5",
    "Accept-Encoding: gzip, deflate",
    "Connection: keep-alive",
    "Upgrade-Insecure-Requests: 1",
);

// 初始化HTTP请求
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

// 发送HTTP请求并获取响应
$response = curl_exec($ch);

// 输出响应
echo $response;

// 关闭HTTP请求
curl_close($ch);
?>

如果需要定时更换User-Agent，可以使用PHP的定时任务工具（如cron）来实现。例如每小时更换一次User-Agent，可以设置一个定时任务，每小时执行一次以下代码：

<?php
// 设置User-Agent列表
$userAgents = array(
    "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36",
    "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36",
    "Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko",
    "Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11.0) like Gecko",
    "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:54.0) Gecko/20100101 Firefox/54.0",
    "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0",
);

// 随机选择一个User-Agent
$userAgent = $userAgents[array_rand($userAgents)];

// 保存User-Agent到文件
file_put_contents("useragent.txt", $userAgent);
?>

然后在采集器中读取保存的User-Agent：

<?php
// 从文件中读取User-Agent
$userAgent = file_get_contents("useragent.txt");

// 设置HTTP请求头部信息
$headers = array(
    "User-Agent: " . $userAgent,
    "Accept-Language: en-US,en;q=0.5",
    "Accept-Encoding: gzip, deflate",
    "Connection: keep-alive",
    "Upgrade-Insecure-Requests: 1",
);

// ...
?>