Variables: Give Your Numbers Names

You’ve been typing numbers like 100 all over your code. To make a whole drawing bigger, you’d have to hunt down every 100 and change each one. There’s a better way: give the number a name. That’s a variable.

A box with a name

A variable is a labeled box that holds a value:

size = 100

Now size means 100. Anywhere you’d type the number, use the name instead. Here’s a square that uses size:

 
 
  

Try it 🎯


    

  1. Change only the first line to size = 200. The whole square grows from one edit!
    2. 

  2. Try size = 50. One change, everything updates.
    3. 

  3. Add a second variable turn = 90 and use t.right(turn). Then change turn to 120 and range(4) to range(3) — a triangle, all from named numbers.
    4. 



That’s the power of a name: change it in one place, and everywhere that uses it follows.


Variables can change


A variable can be updated while the program runs. This line means “take whatever size is now, add 20, and put the answer back in the box”:


size = size + 20


It looks odd at first (how can size equal size + 20?). Read it right-to-left: compute size + 20, then store the result back in size.


Make a spiral


Now the fun part. Start with a short line, draw it, turn, and make the line a little longer each time through the loop. The drawing spirals outward:


   
   
 
 
 
 
 
  

Every loop, length grows by 5, so each side is longer than the last — a square spiral! This is impossible with a fixed number. You need a variable that changes.


Try it 🎯


    

  1. Change t.right(90) to t.right(120). A triangle spiral!
    2. 

  2. Change length = length + 5 to + 2 (grows slowly) or + 10 (grows fast).
    3. 

  3. Change range(40) to range(25) for a smaller spiral.
    4. 



Predict it 🔮


What happens if you change the growth line to length = length + 0 (add nothing)? Guess, then try. (It never grows — so it just draws the same square over and over in place.)


Fix the bug 🐞


This is meant to be a growing spiral, but it just draws one square. The growth line is missing. Add it so each side gets longer:


   
   
 
 
 
 
 
  

(Add     length = length + 5 as the last line inside the loop, indented to match.)


Mix it up 🎨


Change the turn to 91 instead of 90 in your growing spiral. Just one degree more, and the square spiral becomes a smooth, swirling one. (That’s a sneak peek at the next lesson!)


Your mission 🚀


Build a spiral that’s yours. Start from the growing spiral and choose: the turn (90, 120, 144…), the growth amount (+ 1 to + 10), and the number of steps (range(...)). Find a combination you love:


   
   
 
 
 
 
 
  

What you learned today


    

  • A variable stores a value under a name: size = 100.
    • 

  • Use the name anywhere; change it once to update everything.
    • 

  • name = name + n makes a variable grow — which is how you draw spirals.
    • 



Next time is a project: you’ll combine loops and a growing variable into a colorful spiral masterpiece you can show off. 🐢
   
 
 
 
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