INQ241B - Day 4 Notes

Review Circle

Draw a cricle using variables for circumference

function main()
  var circumference = 400
  var number of sides = 36
  for 0 <= i < number of sides do
    ♻turtle → forward(circumference / number of sides)
    ♻turtle → left turn(360 / number of sides)
  end for
end function

What if we wanted to draw many circles?

We could put it inside a loop

function main()
  var number of circles = 10
  for 0 <= j < number of circles do
    var circumference = 400
    var number of sides = 36
    for 0 <= i < number of sides do
      ♻turtle → forward(circumference / number of sides)
      ♻turtle → left turn(360 / number of sides)
    end for
  end for
end function

But all the circles are in the same place and are the same size

Could move the turtle between circles

function main()
  var number of circles = 10
  for 0 <= j < number of circles do
    var circumference = 400
    var number of sides = 36
    ♻turtle → pen up
    ♻turtle → left turn(360 / number of circles)
    ♻turtle → forward(circumference / number of circles)
    ♻turtle → pen down
    for 0 <= i < number of sides do
      ♻turtle → forward(circumference / number of sides)
      ♻turtle → left turn(360 / number of sides)
    end for
  end for
end function

That looks cool, but it’s getting to be a bit of a mess
We can do something to clean it up, functions

Functions

A variables are named values, functions are named code
Currently we have one function, main, it is what is executed when you choose run
To make a new one, click on the script button above your code and choose ‘add new’
From the menu, choose function
Your code disappeared! Don’t worry we can get back to it
What is created is a new function, it has the name ‘do stuff’ and does nothing, let’s fix that
First change the name to draw circle, click on the name to change it to a text field

Now we can put whatever code we want inside this function, let’s put the circle drawing code here

function draw circle()
  for 0 <= i < 36 do
    ♻turtle → forward(400 / 36)
    ♻turtle → left turn(360 / 36)
  end for
end function

Now we can run, or call, this function from the main function
To get back to the main function, click the script button at the top and click on the main function
Delete the code that draw the circle and replace it with the function call
```
▷ draw circle
```
Using functions makes creating large programs easier
You have been doing this, every time you do turtle something, you are running code that someone else wrote

Parameters & Arguments

But now the draw circle ignores the circumference variable
So try to use circumference in the draw circle function
TouchDevelop won’t let you
This is because variables only exist in the function where the var command is used
Note, we could use var circumference but this would create a new variable with the same name but a different value, not what we want
We need a way for the main function to communicate with the draw circle function
Parameters and arguments, again we have seen this with turtle, then thing inside the parentheses
If you click on the function name line, without clicking on the function name, because that changes the function name
There is a + button for ‘add input parameter’
click that and inside the parentheses after the function name there is a text box where you can name the parameter
Name it cicum, just to differentiate it from circumference
A parameter is a variable that gets it’s value set when the function is called.
Use the new parameter
Note, the main function has an error ‘not enough parameters supplied’
Must specify the value, delete and re-add
Can also have multiple parameters and of different types

Quiz

m.socrative.com
Room name ‘INQ241’

Activity

Activity 4