Names for Your Numbers

Try It — Count the Damage

Open your Project 8 program — the big one with all four missions in it. Scroll through it slowly.

How many blocks contain each of these as a bare number?

Now break it

That last question is the real problem. If you missed one, what would happen — and how would you find out?

Learn It — Give the Number a Name

A variable is a name that holds a value. You set it once at the top of your program, then use the name everywhere instead of the number.

Making one

Open the orange Variables category and press Make a Variable. Name it arm up. Two new things appear:

Where variables go

The set blocks go at the very top of the stack — right under the hat, above everything else. Not scattered through the middle of your program. One place, all together, where anyone can find them.

From card to code

You have been writing your positions on your Robot Card in name = number form since Project 7. There was a reason for that. Each line on the card becomes one variable and one set block:

Then use the names

Here is the part that feels like magic the first time: drag the orange oval and drop it into the white number hole of any block.

Read both versions out loud. One is a list of numbers. The other tells you what the robot is doing.

Name things properly

Make it obvious: arm up, not thing2. A name nobody can decode is barely better than a bare number.

Variables can change

Most of your variables hold one value forever — up is always up. But a variable is called a variable because it can vary. Two ways to change one:

Change by is the shorthand for “take what it holds and add this.” You will meet the real use for it in Project 10, once you have a loop to put it in.

Do It — Clean It Up, Then Score

Step 1 — Convert one small program first

Open your Arm Wave program from Project 7. Make variables for the three positions, set them at the top, then drop the ovals into the position blocks in place of the numbers.

Run it. It should behave exactly as before.

• Wave runs the same with variables as it did with numbers

If it behaves differently, you swapped two values. That is the most common mistake here.

Step 2 — Do the leftover-oval check on purpose

Make a variable called not used and never drop it into anything. Now look at your Variables shelf.

Delete it, so the shelf only lists names that are really in use.

Step 3 — Convert your big Project 8 program

This is the real job. Make all your variables, set them at the top, then work down the stack replacing bare numbers with ovals.

• My whole Project 8 program uses variables and still scores the same

Step 4 — Now do the claw change again

Same problem as Try It. Your claw’s closed position drops by 30. Change it.

Compare those two numbers with the ones you wrote in Try It.

Step 5 — Try changing a variable while the program runs

Small experiment. Build this and watch the arm.

The arm moved in three hops instead of one jump. What would you have to do to make it move in thirty small hops?

Hold that thought. Project 10 gives you the tool that makes it three blocks instead of thirty.

Step 6 — Mission 5 — Top Shelf Delivery20 pts

This one asks your arm to reach higher than anything so far. The large red cube is the platform; the small ones go ON TOP OF it.

Where do your red cubes end up after your Mission 2 push? Does that help or hurt you here?

• One Small Red Cube is ON TOP OF the Large Red Cube
• Both Small Red Cubes are up there at the same time

The bonus needs both cubes up there at the same time. Why does that make the second one harder than the first?

Step 7 — Run it five times

Score It — Checkpoint

My score

Make the variable

For each card line, say what you would do in the app.

Read the blocks

Given set arm down to 40 at the top of a stack — what does each of these do?

That last one is a legal block that does something you almost certainly do not want. Say what it actually does.

Can you do it again?

• I can make a variable, name it well, and set its value
• My set blocks live at the top of the stack, right under the hat
• I can turn a name = number card line into a variable and a set block
• I drop variable ovals into blocks instead of typing bare numbers
• My variable names make sense to someone else on my team
• I do the leftover-oval check when I finish converting a program
• I can change a variable’s value part-way through a program

Think about it

Nothing your robot does changed in this project — it drives, grabs, and stacks exactly as it did before. So what actually got better?

Variables fixed the problem of one number appearing in many places. But your program still has the six-step grab sequence built out four separate times. Would variables fix that too? Why or why not?

Your teammate opens your program for the first time. Which version could they work on — the one from Project 8, or this one? What does that tell you about who you are really writing programs for?

Next

Your robot still cannot tell when it has arrived anywhere. It drives for a length of time and hopes.

In Project 10 — Feeling for Things, it gets its first sense: a switch that knows when it has touched something — and the loop that keeps checking.