What are some common mistakes to avoid when copying and pasting PHP code from online sources, and how can code be adapted for specific use cases?

When copying and pasting PHP code from online sources, common mistakes to avoid include not understanding the code's functionality, blindly trusting the code without verifying its security, and not adapting the code for specific use cases. To adapt code for specific use cases, ensure that variable names, input validation, and error handling are tailored to your project's requirements.

// Example of adapting copied code for specific use case
// Original code snippet from online source
$number = $_GET['number'];
$result = $number * 2;
echo $result;

// Adapting code for specific use case
if(isset($_GET['number'])){
  $number = (int)$_GET['number']; // Ensure input is an integer
  if($number > 0){
    $result = $number * 2;
    echo "The result is: " . $result;
  } else {
    echo "Please provide a positive number.";
  }
} else {
  echo "Please provide a number.";
}