1. Procedures

2. What is a procedure?
Often in a program we will need to repeat the same task over and over again.
Rather than repeat writing the code every time we use it, we can use what is called a procedure.

3. Consider our quiz program where we might wish for our user to click a continue button after each question.
That means every question we ask we need to draw the box:
drawfillbox(50,50,150,100)
locatexy(75,75)
put(“continue”)

4. Then after they answer the question, we need to check whether they have clicked the button:
loop
mousewhere(x, y, button)
exit when x<150 and x >50 and y >50 and y<100 and button=1 then
end loop

5. If we are asking only one or two questions, repeating this code is fine.
But if we intend to ask questions, then this isn’t the best way to do things.

6. A procedure is essentially a small program within a program, that we will call whenever it is needed.
A procedure is created to perform a very limited and specific task.
In our example we would create two procedures. The first to create the button, and the second to check whether the button was pressed.

7. Syntax
Just as we declare a variable in order for the program to recognize it later, we must also declare a procedure:
procedure name ( parameters )
instructions
end name
Then when we wish to use the procedure in our program we call it by it’s name.

8. Example procedure create_button drawfillbox(50,50,150,100,blue)
locatexy(75,75)
put(“continue”)
end create_button

9. procedure is_continue_clicked
loop
mousewhere(x, y, button)
exit when x<150 and x >50 and y >50 and y<100 and button=1 then
end loop
end is_continue_clicked

10. Now our program will look like:
put “What is your name”
get name
create_button
is_continue_clicked
put “What is your age”
get age
createbutton

11. Special notes on procedures
Procedures must be declared at the beginning of the file!
You may call a procedure within a procedure but it must have already been declared. (See example B)
Two or more procedures may not call each other!

12. Example B procedure terrence put “Hi my name is Terrence” end terrence
procedure philip
terrence
put “Hi Terrence my name is Philip”
end philip

13. Example C procedure one two % calls procedure two
end one % but two hasn’t been
% declared yet
procedure two
one % calls procedure one
end two