What common pitfalls should PHP beginners be aware of when defining variables?

One common pitfall for PHP beginners when defining variables is using invalid variable names, such as starting with a number or containing special characters. Another pitfall is not initializing variables before using them, which can lead to errors or unexpected behavior. Beginners should also be aware of variable scope, as variables defined outside of a function may not be accessible within the function.

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

// Initializing variables
$number = 5;
$result = $number * 2;
echo $result;

// Variable scope
$globalVar = "I am a global variable";

function testFunction() {
    // This will cause an error as $localVar is not defined within the function
    echo $localVar;
}

testFunction();