For a funtion to process on require some arguments to be passed to it. This is not the case always, some funtions require no arguments. such funtion outputs the same message whenever it is called on. This is illustrated in the example below.

Whenever this function is called on, it outputs the same message. It takes no arguments and doesn't return anything.

The "return" statement is used to send the result to the function. Here in this case the result is calculated value of the purchase (which is number of items purchased multiplied by price)

A function can be called dynamically in the same way we access dynamic variables. We can treat an expression's name as a funtion name and thus can call it.

When we want to access some important information which are outside the function, and without using arguments. Then we have to use the "global" statement.

Here we have used the global statement to tell the function that "$exchange_rate" is declared outside the the function. If we wont declare like this then the function would have returned zero, since $exchange_ratewould have been "NULL".