What are common beginner mistakes when defining variables in PHP?

Common beginner mistakes when defining variables in PHP include using invalid variable names (e.g. starting with a number or containing special characters), not initializing variables before using them, and overwriting variables unintentionally. To avoid these mistakes, make sure to follow variable naming rules, always initialize variables before use, and be mindful of variable scope to prevent accidental overwriting.

// Incorrect variable name starting with a number
$1stVariable = "Hello";

// Correct variable name
$firstVariable = "Hello";

// Variable not initialized before use
$number;
echo $number; // Notice: Undefined variable: number

// Initializing variable before use
$number = 5;
echo $number;

// Accidental variable overwriting
$number = 5;
$number = "Five";
echo $number; // Outputs: Five