More about the Syntax

The general form of the definition of a function is as follows:

function func_name $[$ (params) $]$ : ret_type ;
begin
...
end

In this notation, $[$ and $]$ encloses a section that is optional. This means the formal parameters are optional.

It is important that the programmer remember to assign a returned value to the name of a function. The Pascal compiler does not check and make sure a function always returns a value! In other words, the following function is perfectly correct:

function useless : integer;
  begin
    writeln('I am useless.')
  end;

What do you think the following code prints?

writeln(useless);

Because the function definition of useless does not specify any particular value to return (as an assignment to useless), its actual returned value is undetermined. This means there is a value returned every time useless is called, it's just that we can not determine what that value is. This is not to say that useless returns a random value because the value returned by useless does depend on the useage of useless and other factors in the program.