INQ241A - Day 3 Notes

Review Polygon

Want to draw a hexagon withh circuference 400:
Need to calculate the move distance: 400 / 6 = 66.67

Need to calculate the turn angle: 360 / 6 = 60

function main()
  for 0  <= i < 6 do
    ♻turtle → forward(66.67)
    ♻turtle → left turn(60)
  end for
end function

Arithmetic

Now, what if we want a pentagon instead
Need to change the iterations, the forward distance, and the turn angle turning the same amount 5 times

But there is a better way, let the program do the math

function main()
  for 0  <= i < 6 do
    ♻turtle → forward(400 / 6)
    ♻turtle → left turn(360 / 6)
  end for
end function

Now we can change the shape just by changing all of the sixes to fives
Anywhere you can put a number, you can put a mathmatical equations as well

Variables

But changing all three of those variables is a bit of pain, and prone to making mistakes in a large program
Again, there is a better way, named values, also called variables
We can name the 5, according to what it represents, in this case the number of sides

Replace all of the fives with the variable name

function main()
  var number of sides := 5
  for 0  <= i < number of sides do
    ♻turtle → forward(400 / number of sides)
    ♻turtle → left turn(360 / number of sides)
  end for
end function

And changing the shape is as simple as changing one number in the program
Added bonus, it’s easier to read
We can make it even more easy to read by using another variable

Replace 400 with the name circumference

function main()
  var number of sides := 5
  var circumference := 400
  for 0  <= i < number of sides do
    ♻turtle → forward(circumference / number of sides)
    ♻turtle → left turn(360 / number of sides)
  end for
end function

Now it is also easy to change the size of the polygon
Note, the order matters; must declare the variable’s value before using the variable name
Can also use variables names in the definition of other variables names

The code would be even more readble with variables for the edge length and turn angle

function main()
  var number of sides := 5
  var circumference := 400
  var edge length := circumference / number of sides
  var turn angle := 360 / number of sides
  for 0  <= i < number of sides do
    ♻turtle → forward(edge length)
    ♻turtle → left turn(turn angle)
  end for
end function

Quiz

socrative.com.
Room name ‘INQ241’

Activity

Activity 3