Here's an example PHP code to calculate the resistance value of a resistor based on its color bands:

<?php

$color_codes = [
    'black' => 0,
    'brown' => 1,
    'red' => 2,
    'orange' => 3,
    'yellow' => 4,
    'green' => 5,
    'blue' => 6,
    'violet' => 7,
    'gray' => 8,
    'white' => 9
];

$first_band = 'brown'; // replace with the actual color of the first band
$second_band = 'black'; // replace with the actual color of the second band
$third_band = 'red'; // replace with the actual color of the third band

$multiplier = 1;
$tolerance = 0.05;

$first_digit = $color_codes[$first_band];
$second_digit = $color_codes[$second_band];
$third_digit = $color_codes[$third_band];

$ohms = ($first_digit * 10 + $second_digit) * $multiplier;
$ohms_string = number_format($ohms, 2);

echo "Resistance value: {$ohms_string} ohms (+/-{$tolerance})";

?>

Here's an example code for sending and receiving request cookies using JavaScript:

Sending a request cookie:

To send a request cookie, you simply include it in the headers of the HTTP request. Here's an example using the fetch API:

fetch('/api/data', {
  headers: {
    'Cookie': 'name=value'
  }
})
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error(error));

This code sends a GET request to /api/data with a request cookie named name and value value. The fetch API includes the cookie in the headers of the request, using the Cookie header.

Receiving a request cookie:

To receive a request cookie, you can access it in the headers of the HTTP response. Here's an example using the express framework in Node.js:

const express = require('express');
const app = express();

app.get('/api/data', (req, res) => {
  const myCookie = req.headers.cookie.split(';').find(cookie => cookie.trim().startsWith('name='));
  if (myCookie) {
    const cookieValue = myCookie.split('=')[1];
    res.send(`Received cookie value: ${cookieValue}`);
  } else {
    res.send('No cookie found');
  }
});

app.listen(3000, () => console.log('Server listening on port 3000'));

This code defines an HTTP server that listens for GET requests to /api/data. When a request is received, the server checks the headers of the request for a cookie named name. If the cookie is found, the server extracts its value and sends a response containing the value. Otherwise, the server sends a response indicating that no cookie was found.

Note that request cookies are set by the client in the HTTP request headers, and can be retrieved by the server as shown above. The specific method for setting request cookies may vary depending on the client-side technology being used.

Here is an example code for setting and getting response cookies using JavaScript:

Setting a response cookie:

// Set a cookie that expires in 7 days
document.cookie = "name=value; expires=" + new Date(Date.now() + 604800000).toUTCString() + "; path=/";

This code sets a cookie with the name "name" and value "value", with an expiration time of 7 days from the current time. The path attribute is set to "/" to ensure the cookie is available to all pages on the website.

Getting a response cookie:

function getCookie(name) {
  const cookieString = document.cookie;
  const cookieArray = cookieString.split(';');
  for (let i = 0; i < cookieArray.length; i++) {
    const cookie = cookieArray[i].trim();
    if (cookie.startsWith(name + '=')) {
      return cookie.substring(name.length + 1, cookie.length);
    }
  }
  return null;
}

// Example usage
const myCookie = getCookie('name');
if (myCookie) {
  console.log('Cookie value:', myCookie);
} else {
  console.log('Cookie not found');
}

This code defines a function getCookie that takes a cookie name as an argument and returns the value of the cookie, or null if the cookie is not found. The function splits the document.cookie string into an array of individual cookies, then loops through each cookie to find the one with the specified name. If found, the function returns the cookie value. Otherwise, it returns null.

Note that response cookies are set by the server in the HTTP response headers, and can be retrieved by the client as shown above. The specific method for setting response cookies may vary depending on the server-side technology being used.

Here is a basic example of code for a browser cookie banner that notifies users that your website uses cookies and asks for their consent:

HTML code: 

<div id="cookie-banner">
  <p>This website uses cookies to ensure you get the best experience on our website. By continuing to use this site, you consent to our use of cookies. For more information, please see our <a href="#">Cookie Policy</a>.</p>
  <button id="accept-cookies">I accept</button>
</div>

CSS code: 

#cookie-banner {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  background-color: #f5f5f5;
  border-top: 1px solid #ccc;
  padding: 20px;
  text-align: center;
  font-size: 14px;
}

#accept-cookies {
  background-color: #4CAF50;
  border: none;
  color: white;
  padding: 10px 20px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 14px;
  margin-top: 10px;
  cursor: pointer;
}

JavaScript code:

const cookieBanner = document.querySelector('#cookie-banner');
const acceptCookiesBtn = document.querySelector('#accept-cookies');

function hideCookieBanner() {
  cookieBanner.style.display = 'none';
  localStorage.setItem('cookieAccepted', true);
}

if (localStorage.getItem('cookieAccepted') === 'true') {
  cookieBanner.style.display = 'none';
} else {
  acceptCookiesBtn.addEventListener('click', hideCookieBanner);
}

This code creates a banner at the bottom of the page that informs the user about the use of cookies and provides a button to accept them. When the user clicks the button, the banner is hidden and a cookie is stored in the user's browser to remember their consent. If the user has already accepted cookies, the banner is not displayed.

Note that this is just a basic example, and you may need to customize the code to fit the specific needs of your website and comply with applicable privacy regulations.