What are some best practices for structuring PHP code to avoid issues with duplicate data or incorrect outputs?

To avoid issues with duplicate data or incorrect outputs in PHP code, it is essential to follow best practices such as using functions to encapsulate reusable code, implementing proper error handling, and organizing code into logical modules or classes. By structuring code in a clear and organized manner, you can reduce the likelihood of introducing bugs or inconsistencies in your application.

// Example of using functions to encapsulate reusable code
function calculateSum($num1, $num2) {
    return $num1 + $num2;
}

$sum = calculateSum(5, 3);
echo $sum;