What are some common errors to avoid when working with PHP arrays and file handling?

One common error to avoid when working with PHP arrays is attempting to access an array element that does not exist, which can lead to undefined index errors. To prevent this, always check if the key exists before trying to access it using functions like `isset()` or `array_key_exists()`. Similarly, when working with file handling in PHP, a common mistake is forgetting to check if a file exists before trying to open or read from it. This can result in errors or unexpected behavior. To avoid this, always use functions like `file_exists()` to verify the existence of a file before proceeding with file operations.

// Avoiding undefined index error
if(isset($array['key'])) {
    // Access the array element safely
    $value = $array['key'];
}

// Avoiding file handling errors
$filename = 'example.txt';
if(file_exists($filename)) {
    // Open and read from the file
    $file = fopen($filename, 'r');
    $content = fread($file, filesize($filename));
    fclose($file);
} else {
    echo "File does not exist.";
}