Procedures and functions are the topics today, so listen up! After going through this tutorial, you will never want to give up programming again!

What are Procedures and Functions?

First of all, what is a procedure? Well, let's say you've got a job as a dishwasher. The process of washing a dish could be:

1. Dip the dish into the water
2. Cover every inch of the dish with soap
3. Rinse and dry the dish

Now about functions. A function is just like a procedure except that it returns a value. For example, somebody may ask you to count the number of chairs in a hall. You first step in, count, then return the number of chairs in the hall back to the person who first asked you. That is a function. A function simply returns another value back into the program, such as complex calculation results, the position of the mouse cursor, or the number of times an atomic bomb had dropped onto the Earth. Functions can report almost anything. Numbers, strings, characters, anything! And if you want to, you can use functions replace procedures completely! Isn't that great?

Scope of Variables

How procedures and functions are implemented

Procedures are declared using the procedure keyword, as you can see below. The name of the procedure comes first, followed by a semicolon, then the contents of the procedure.

  procedure WhyMe;

    var
      i: integer;

    begin
      for i := 1 to 10
        Writeln('Why Me?!');
    end;

  begin
    WhyMe;
    Writeln('That was my true feelings regarding Exams');
  end.

Functions, on the other hand, cannot be used just like that because they return a value back to the program instead of just doing things. For instance, we may have a function which acts like this:

  function AddEmUp : integer;
    begin
      AddEmUp := a + b + c;
    end;

  begin
    a := 5;
    b := 9;
    c := 4;
    Writeln(AddEmUp);
  end.

Procedures and functions would have been dreadfully boring and unflexible if it wasn't for a great feature called parameters. You can use parameters to pass values to the procedure or function to use. For example:

  function AddEmUp2( x, y, z: integer ) : integer;
    begin
      AddEmUp2 := x + y + z;
    end;

  begin
    Writeln(AddEmUp2(2, 3, 5));
  end.

  procedure PrintEm( x, y, z: integer );
    begin
      Writeln(x);
      Writeln(y);
      Writeln(z);
    end;

The final example program...

1: program AddEmUpAgain;
2:
3:   function AddEmUp( a, b, c: integer ) : integer;
4:     begin
5:       AddEmUp := a + b + c;
6:     end;
7:
8:   procedure PrintIt( a, b, c: integer );
9:     begin
10:      Writeln('The sum of a, b, and c is ', AddEmUp(a, b, c), '.');
11:    end;
12:
13:  begin
14:    PrintIt(2, 3, 4);
15:  end.

The sum of a, b, and c is 9.

Although it looks complicated, this is actually a very simple program. It does absolutely nothing but to add three numbers together! Is that dumb or what?

• Line 3 - This declares the function AddEmUp, which takes three parameters and adds them up.
• Line 5 - The only line of AddEmUp, it justs returns the sum of parameters a, b, and c.
• Line 8 - Declares procedure PrintIt, which also accepts three parameters.
• Line 10 - This line simply prints out the correct message by calling AddEmUp and passing it the three parameters.
• Line 14 - This single line starts the whole ball rolling!

Well, that was the great example program of the day! But this topic is far from over. Here are the tips and rules we couldn't fit into the text without making it ridiculously boring. (As if it wasn't already...)

1. You must declare a function or a procedure before it is used. For example, in the example program above, you can't just put the procedure on top of the function because PrintIt needs to use AddEmUp, it needs to be declared first.
2. However, if the world somehow gives you a reason to use a procedure before you declare it, you can use the forward keyword. Find out from your nearest F1 key!
3. What happens if you provide more parameters than a procedure or function needs? Well, when you do so (or vice versa), the compiler simply gives you an error, so go on and experiment! (Em, don't play too much though...)
4. No, you can't re-declare constants in a new procedure - Why would you anyway?
5. Procedures and functions are a very important part of structured programming. Suffice it to say that is you don't learn structured programming now, you'll never make it big in the future.
6. No, there will not be another Bill Gates analogy for this tutorial.

The Final Chapter is coming