Question:What is recursive function? 

A recursive function is a function that calls itself during its execution. This enables the function to repeat itself several times, outputting the result and the end of each iteration. Below is an example of a recursive function. 

function Count (integer N)     
if (N <= 0) return "Must be a Positive Integer";     
if (N > 9) return "Counting Completed";     
else return Count (N+1); 
end function

Question:What are class and object? 

Class: Classes are intended to represent those real-life items that coder like to manipulate within an application.

Object: A class provides a basis from which you can create specific instances of the entity the class models, better known as object.That means, an instance of class is called object . Such as $employee = new Employee();

Question:What are the functions used for file upload? 

bool move_uploaded_file ( string $filename , string $destination )
bool copy ( string $source , string $dest [, resource $context ] )