How can using the assignment operator instead of the comparison operator in PHP lead to errors in data validation?

Using the assignment operator "=" instead of the comparison operator "==" in PHP can lead to errors in data validation because it assigns a value to a variable instead of comparing two values. This can result in unintended consequences, such as overwriting data or not properly validating user input. To fix this issue, always use the comparison operator when comparing values for data validation.

// Incorrect comparison using assignment operator
$age = 18;
if ($age = 18) {
    echo "You are 18 years old.";
}

// Correct comparison using comparison operator
$age = 18;
if ($age == 18) {
    echo "You are 18 years old.";
}