Writing A Simple Procedure; Procedures With Parameters - AMSTRAD cpc 6128 User Instruction

Writing
Cl
Simple Procedure
It
is easy to visualise that ifthe movements:
fd 60 rt 90
.... were to be repeated 4 times each, a square with sides of60 units would be drawn.
The same effect can be achieved by writing a simple formula:
repeat 4 [fd 60 rt 90]
Clear the screen and then try typing this in to check what happens.
To make this formula into a new procedure called '5 q
U
are', type:
to square
repeat 4 [fd 60 rt 90]
end
Dr. LOGO will now understand '5qua re', and each time it encounters the word
'5 q
U
are' it will draw a square on the screen. We could have given this procedure
any name, but we chose '5 qu a r e'toremind us what it does.
Dr. LOGO allows us to type in a whole set of commands together so the instructions:
square rt 45 square
.... will draw two squares, the second at a 45 degrees angle to the first.
Procedures with parameters
It
is possible to make a procedure to which we can say 'how much', in the same way
that we can say 'how much' to a built-in procedure. To make a procedure thatwill
draw squares of different sized sides, the definition of' 5 q
U
are' can be altered to:
to squareanysize :side
repeat 4 [fd :side rt 90]
end
You will notice that the variable : 5
i
de starts with a colon. This indicates to Dr.
LOGO that: 5
i
de is a variable rather than a command.
When we use the procedure 5 q
U
are any 5 ; z e, the variable : 5 ; d e must have a
value. Hence the instruction 5 q
U
are any 5 ; z e 1
50
would produce a square
with sides of150 units.
Chapter 6 Page 4 Introduction to Logo