INQ241A
Mobile Apps

Day 3 Notes

Variables

Review Variables

    function main()
      var distance := 100
      ♻turtle → forward(distance)
      ♻turtle → back(distance)
      ♻turtle → right turn(90)
      ♻turtle → forward(distance)
      ♻turtle → back(distance)
    end function

Reusing Variables

It is also possible to change the value of a variable after it has been declared

So if we wanted to draw an L

function main()
  var distance := 100
  ♻turtle → forward(distance)
  ♻turtle → back(distance)
  ♻turtle → right turn(90)
  distance := 50
  ♻turtle → forward(distance)
  ♻turtle → back(distance)
end function

This is why they are called variables, the value can vary
Note, when changing the value, don’t use var
Also note, order still matters

Updating Variables

But what if we want to change the size of drawing?
Need to change two variables, one dependent on the other
We can do better

Can update a variable using its own value

function main()
  var distance := 100
  ♻turtle → forward(distance)
  ♻turtle → back(distance)
  ♻turtle → right turn(90)
  distance := distance / 2
  ♻turtle → forward(distance)
  ♻turtle → back(distance)
end function

The horizontal line will always be half the length of the first one
So now can change the distance variable’s initial value and the entire drawing will change size

Accumulating Variables

We can also update variables inside of a loop

Here is a neat drawing that uses a loop

function main()
  var distance = 100
  var angle = 5
  for 0  <= i < 360 / angle do
    ♻turtle → forward(distance)
    ♻turtle → back(distance)
    ♻turtle → left turn(angle)
  end for
end function

Updating variables inside a loop causes it to accumulate values

For example, changing the distance each iteration

function main()
  var distance = 5
  var angle = 5
  for 0  <= i < 360 / angle do
    ♻turtle → forward(distance)
    ♻turtle → back(distance)
    ♻turtle → left turn(angle)
    distance := distance + 5
  end for
end function

This means that the length of each line will be 5 units longer than the last line drawn

Quiz

socrative.com.
Room name ‘INQ241’

Activity

Activity 4