Pet Pal I

Review — where we got to 5 min

The Quiz Show is finished and shared. Two things from it come straight back today.

• when this sprite clicked — the button hat from last week.
• <() < ()> and <() > ()> — comparing a variable with a number.

Quick-fire

Every project you have written does nothing at all until somebody presses something. What would make one change on its own?

Today’s Topic 3 min

• A variable that goes down on its own, using wait inside forever
• A second script that watches that variable and reacts
• Two costumes standing for two moods
• A bowl you click to put the number back up

Learning outcome

By the end of this lesson you will be able to:

1. Make a number change by itself, at a speed you choose.
2. Make a sprite react when that number gets low.
3. Let the player push the number back up by clicking something.

Learnt — a number with a clock on it 28 min

1 · Wait, take one off, repeat

You know forever, and you know wait (1) seconds. Put one inside the other and you have a clock.

1. Make a variable called food. Leave it showing.
2. On the pet, start with when flag clicked and set [food v] to (10).
3. Drag out forever from Control.
4. Put wait (1.5) seconds inside it.
5. Under that, still inside, put change [food v] by (-1).
6. Press the flag, then take your hands off the keyboard and watch.

when flag clicked
set [food v] to (10)
forever
  wait (1.5) seconds
  change [food v] by (-1)
end
            

2 · The pet notices

Now the number can get low, and nothing happens. Add a second script — running at the same time — whose only job is to look at it.

when flag clicked
forever
  if <(food) < (5)> then
    switch costume to [dog2-c v]
    say [I am hungry!] for (1) seconds
  end
end
            

<() < ()> is the less-than block, next to the greater-than one you used for the pass mark. It sits in Operators.

3 · The bowl

A pet you cannot feed is not a game, it is a countdown. The bowl is a sprite with the button hat you built last week.

1. Add a Bowl sprite and put it in a bottom corner.
2. Give it when this sprite clicked.
3. Under that, put start sound [Chomp v].
4. Then change [food v] by (3).
5. Run it and click the bowl. The number jumps up.

when this sprite clicked
start sound [Chomp v]
change [food v] by (3)
            

That is the whole game already. One script takes food away on a clock, one gives it back on a click, and a third looks at the number and decides what face to wear.

Basic — build your pet 25 min

One script at a time, and test after every one by pressing the flag and waiting.

Step 1 — the room

1. New project, cat deleted.
2. Choose an indoor backdrop. Room 1 or Bedroom 1.
3. Add an animal sprite with at least two costumes. Dog2, Frog and Hedgehog all work.
4. Look at the Costumes tab and pick the TWO that look most different. Write their names down. Dog2’s first two are almost the same picture; its third has a raised eyebrow and reads as worried from across the room.

Step 2 — the clock

1. Make the food variable.
2. Build the flag stack with the forever loop in it.
3. Press the flag and watch for twenty seconds without touching anything.
4. The number should reach 0 and keep going negative. That is fine for now.

Step 3 — the bowl

1. Add a bowl or a food sprite and put it in a corner.
2. Give it a flag stack that puts it in place, so it never wanders.
3. Give it the clicked stack.
4. Play for a minute. Try to keep the number above 5.

Step 4 — the mood

1. On the pet, add the second flag stack with the if in it.
2. Use your own costume names in the switch-costume block.
3. Add an else half that switches back to the happy costume.
4. Play again. The face should follow the number both ways.

Step 5 — make it yours

1. Change what the pet says when it is hungry.
2. Add a sound to the bowl and a different one to the pet.
3. Try feeding by 2 instead of 3 and see whether the game gets better or worse.

Your pet, your room

Throw mine away. Pick your own animal, your own room and your own food.

• A different pet sprite from the one in the lesson.
• A backdrop that suits where it lives.
• A food sprite that suits the animal.

A face you can read across the room

Hide the number. Somebody standing behind you should still know whether the pet needs feeding.

• The variable’s tick box is unticked, so no number shows.
• Happy and hungry look completely different.
• It changes back both ways, not just one.

Find the right speed

Your pet is either exhausting or boring. Change three numbers until it is neither, and write down what you chose.

• You have tried at least three different wait times.
• You have tried at least two different feeding amounts.
• You can say which combination you kept and why.
• You can play for a minute without either panicking or getting bored.

A bowl that can be full

Right now a player can click the bowl thirty times and go and make a drink. Stop them: feeding a full pet should do nothing but say so.

• The food never goes above 10, however many times the bowl is clicked.
• Clicking a full bowl says something rather than doing nothing silently.
• Feeding still works normally when the pet is hungry.

when this sprite clicked
if <(food) < (10)> then
  start sound [Chomp v]
  change [food v] by (3)
else
  say [The bowl is already full.] for (2) seconds
end
            

Summary 4 min

Today a project kept working while nobody was touching it.

1. wait (1) seconds inside forever is a clock.
2. One script changes the number; another one only ever looks at it.
3. Two costumes are enough to show a mood.
4. A bowl is a sprite with a clicked hat and one change block.

Clock loop

A forever loop with a wait in it, so something happens at a steady speed.

Less than

Asks whether the left number is smaller than the right one.

Mood

A costume chosen by looking at a variable, not by the player.

Balance

Choosing the numbers so the game is neither too easy nor too hard.

Next lesson: what happens when the food reaches nothing, and how many days you can keep the pet alive.