Functions That Take Inputs

Last time you taught the turtle a trick with def square(): and used it again and again. But it always drew the same size square. Today you give your functions a knob — an input you can change every time you call them. That’s called a parameter, and it makes functions enormously more powerful.

A function with a knob

Put a name inside the parentheses, and use it inside the function. Here, size is the knob:

The 40 in square(40) becomes size inside the function. Want a different size? Just change the number you pass in.

Try it 🎯

1. Change square(40) to square(120). Big square!
2. Below it, add square(25). (It draws on top — we’ll spread them out next.)

One function, many sizes

Now place a few different sizes around the screen with goto:

Same square function, three different sizes. One trick, endless variety.

Predict it 🔮

What do you think square(0) draws? And square(-50)? Guess, then try each. (0 draws nothing — a zero-size square; a negative number makes the turtle go the other way!)

Two knobs: size and color

A function can take more than one parameter. Separate them with a comma. Here square takes a size and a color:

Now each call says how big and what color. The order matters: the first number is size, the second is color.

The big combo: a loop that turns the knob

Here’s where it clicks. A loop can call your function with a different value each time. This draws a row of growing dots — the loop changes the size on every call:

Five dots, each bigger than the last, all from one dot function called in a loop. Function + parameter + loop together — that’s real programming power.

Fix the bug 🐞

This square is supposed to take a size, but the call forgot to pass one, so it crashes. Give the call a number:

(A function with a parameter needs a value when you call it. Change square() to square(70).)

Your mission 🚀

Write a triangle(size, color) function (3 sides, turn 120, filled with the color), then call it twice with different sizes and colors:

What you learned today

• A parameter is an input to a function: def square(size):.
• Call it with a value: square(40) — change the value, change the result.
• Functions can take several parameters: square(size, color).
• A loop can call a function with a different value each time — combining everything you know.

Next time we add surprise: randomness, so your art comes out different every single time you press Run. 🐢