Pet Pal II

Review — where we got to 5 min

Your pet gets hungry on a clock and you can feed it. Two ideas from before come back.

• forever with a wait (1) seconds in it — the clock you built last week.
• A best variable set on the green flag only, from the Quiz Show.

Quick-fire

Your pet’s food went to −7 last week and nobody noticed. Why is that bad?

Today’s Topic 3 min

• wait until <> — a block that sits still until something becomes true
• An ending: a sad costume, a sentence, and stop all
• A days counter on a clock of its own
• A best run that survives the next player

Learning outcome

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

1. End the game the moment a variable reaches zero.
2. Count how long the player lasted and read it out at the end.
3. Keep the best run so far, so the next player has something to beat.

Learnt — zero, and how long you lasted 28 min

1 · The block that waits for a thing to be true

You could write this with a forever loop and an if in it — you did exactly that for the Quiz Show referee. There is a block that means the same thing in one line.

1. Open Control.
2. Find wait until <>, under the wait block.
3. Drop <() = ()> into its diamond.
4. Drag (food) into the left side and type 0 in the right.
5. Put it under a green-flag hat on its own, with the ending under it.

when flag clicked
wait until <(food) = (0)>
switch costume to [dog2-c v]
say [You forgot about me...] for (3) seconds
stop [all v]
            

2 · The score is time

This game has no points. What the player is trying to do is last, so the score is how long they lasted — which is another variable on another clock.

when flag clicked
set [days v] to (0)
forever
  wait (3) seconds
  change [days v] by (1)
end
            

Three scripts are now running at once on the same sprite. One empties the food, one fills the days, one waits for the end. None of them knows about the others.

3 · The ending says what happened

“Game over” tells the player nothing. Put the number in the sentence with join [ ] ( ), the same block the Quiz Show used.

when flag clicked
wait until <(food) = (0)>
if <(days) > (best)> then
  set [best v] to (days)
end
switch costume to [dog2-c v]
say (join [You looked after me for ] (days)) for (4) seconds
stop [all v]
            

Basic — a game with an ending 25 min

Carry on from last week’s pet. Four new scripts, tested one at a time.

Step 1 — the ending

1. Add a new green-flag stack to the pet.
2. Put wait until <(food) = (0)> in it.
3. Under that, the sad costume, a sentence, and stop all.
4. Test it by NOT feeding the pet. Time how long that takes.

Step 2 — the days

1. Make a variable called days and show it.
2. Add another green-flag stack with the day clock in it.
3. Play a proper game and see how far you get.

Step 3 — the ending says the number

1. Open your ending script and swap the say block for a join [apple ] [banana] one.
2. Drag (days) into the right half of the join.
3. Play again and check the number in the sentence matches the one on screen.

Step 4 — the record

1. Make a variable called best.
2. Set it to 0 on ONE green-flag stack, and nowhere else.
3. Add the comparison at the top of the ending script.
4. Play three games without pressing the flag in between.

Step 5 — tune it

1. Decide how long a really good run should be. Write the number down.
2. Change the day clock until a good player gets close to it.
3. Play it three times without trying hard. If you never come close to losing, it is too easy.

An ending worth reaching

Your game stops. Make it FINISH: a face, a sentence with the number in it, and a reason to try again.

• The pet changes to show what happened.
• The sentence contains the number of days.
• It stays on screen long enough to read.

Warn them before it is too late

Losing should never be a surprise. Make the pet show it is in trouble while there is still time to save it.

• The warning starts before the food is gone.
• It stops when the player feeds the pet.
• It is different from the ordinary hungry face.

A record to beat

Put a record on the screen, keep it between games, and make the pet say something special when somebody breaks it.

• The record is on screen from the very first game.
• It does not reset when a new game starts.
• Breaking it gets its own message.
• Not breaking it says what the record still is.

A pet that grows

Every day your pet gets a little bigger and a little hungrier, so a run that was easy at the start becomes impossible.

• The pet visibly grows as the days go by.
• It eats more each day than it did the day before.
• Nobody can survive for ever, however fast they click.
• The first thirty seconds are still easy.

when flag clicked
set [appetite v] to (1)
forever
  wait (0.8) seconds
  repeat (appetite)
    change [food v] by (-1)
  end
end
            

when flag clicked
forever
  wait (3) seconds
  change [days v] by (1)
  change [appetite v] by (1)
  change size by (8)
end
            

Summary 4 min

A game needs an ending. Today yours got one, and a score to go with it.

1. wait until <> sits still until something becomes true.
2. The ending changes the face, says the number, then stops everything.
3. When the point of a game is to last, the score is a clock going up.
4. A record is set on the green flag and updated only when it is beaten.

Wait until

A block that pauses its script until the question in it becomes true.

Game over

The moment a rule is broken. It needs a face, a sentence and a stop.

Day counter

A variable that goes up on a clock. The score of a survival game.

Record

The best anybody has managed. It outlives a single game.

Next lesson: three things to look after instead of one, and a face that comes from the worst of them.