One box, two places

Challenge 3 of 12

Here is why a box is worth having. level is written twice — small in the header and large below it — but there is only one place to change it, and both follow. That is the whole point of a name.

Set level to match the target.

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Set level to match the target.

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Lesson Whole Numbers

A variable is a named box that holds a value. You make one like this: var score = 10; The word var says "make a new box", score is the name you chose for it, and 10 is what goes inside.

From then on, writing score anywhere means "whatever is in that box" — here, 10. That is the whole idea, and the rest of this course is built on it.

Why bother, when you could just type 10? Because a box can be used in more than one place. Write score three times and all three show the same number, and changing the one var line changes all three at once. You never have to hunt for every copy.

To see what a variable holds, draw it: write(score, 20, 40); puts the value onto the canvas. It is the same write() you used in Course 1, but with a variable name instead of words in quote marks. No quotes, because you want what is inside the box, not the word score itself — write("score", 20, 40); would draw the five letters s-c-o-r-e.

Names are up to you, but choose ones that say what they hold: score, lives, top. In this topic you will set values, name boxes yourself, and keep several at once.