What is the potential issue with using undefined variables in PHP scripts?

Using undefined variables in PHP scripts can lead to errors or unexpected behavior in your code. To avoid this issue, it is recommended to always initialize variables before using them to ensure they have a value assigned. This can be done by setting default values or checking if the variable is set using isset() before using it in your code.

// Example of initializing a variable before using it
$variable = ""; // Initialize variable with default value

// Check if the variable is set before using it
if(isset($variable)) {
    // Use the variable here
    echo $variable;
}