Times-Table Challenge II

Review — where we got to 5 min

• (pick random (1) to (10)), kept in a and b, makes a new question every time.
• (join (a) (join [ × ] (b))) glues the question together.
• <(answer) = ((a) * (b))> lets Scratch check it.

Quick-fire

Your round asks five questions. How could it keep asking for exactly one minute instead?

Today’s Topic 3 min

• (timer) and reset timer — Scratch’s own stopwatch
• (round ((60) - (timer))) — a countdown in whole seconds
• repeat until — a loop that stops itself
• Three lives, and a round that ends on time OR on lives

Learning outcome

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

1. Time something with the timer, and show the time left.
2. Loop until something is true, instead of a fixed number of times.
3. End a round when time runs out or when the lives do.

Learnt — a clock and three lives 28 min

1 · Scratch’s own stopwatch

A stopwatch counts up from 0. Scratch has one built in, and it is always running.

1. Click Sensing. It is the light blue drawer.
2. Find (timer) near the bottom. Tick the box beside it.
3. A box appears on the Stage. Watch it count up in seconds.
4. Click reset timer, just above it. The box jumps back to 0.

2 · Time left, in whole seconds

Players want to see how long is left, not how long has gone. That is a take-away sum.

((60) - (timer))
              

(round ((60) - (timer)))
              

(round ()) is in Operators. It turns 56.73 into 57 and 56.2 into 56. A whole number is easier to read at speed.

3 · A loop that stops itself

repeat (5) counts to 5 and stops. We do not know how many questions fit in a minute. So we need a different loop.

repeat until in Control runs its inside again and again. Before each go, it checks its diamond. When the diamond is true, it stops.

when flag clicked
reset timer
repeat until <(timer) > (10)>
  set [time left v] to (round ((10) - (timer)))
end
set [time left v] to (0)
say [Time's up!] for (2) seconds
            

4 · Three lives

A game you cannot lose is not much of a game. Give the player three lives. A wrong answer takes one away.

1. Make a variable called lives.
2. At the start, set [lives v] to (3).
3. In the else half, add change [lives v] by (-1).
4. Make the loop repeat until <(lives) = (0)>.

when flag clicked
set [score v] to (0)
set [lives v] to (3)
repeat until <(lives) = (0)>
  set [a v] to (pick random (1) to (10))
  set [b v] to (pick random (1) to (10))
  ask (join (a) (join [ × ] (b))) and wait
  if <(answer) = ((a) * (b))> then
    change [score v] by (1)
  else
    change [lives v] by (-1)
    say (join [It is ] ((a) * (b))) for (1) seconds
  end
end
say (join [Out of lives! Score: ] (score)) for (4) seconds
            

5 · Time OR lives

Our round should end when the time is up or the lives are gone. The <<> or <>> block in Operators joins two diamonds. It is true if either side is true.

repeat until <<(timer) > (60)> or <(lives) = (0)>>
end
            

6 · The clock needs its own script

ask [] and wait stops its script until you press Enter. If time left lives in that same loop, it freezes while you think.

So the clock gets a script of its own. Two scripts run at the same time — you did this in Level 1.

when flag clicked
set [score v] to (0)
set [lives v] to (3)
reset timer
broadcast [clock v]
repeat until <<(timer) > (60)> or <(lives) = (0)>>
  set [a v] to (pick random (1) to (10))
  set [b v] to (pick random (1) to (10))
  ask (join (a) (join [ × ] (b))) and wait
  if <(answer) = ((a) * (b))> then
    change [score v] by (1)
  else
    change [lives v] by (-1)
    say (join [It is ] ((a) * (b))) for (1) seconds
  end
end
say (join [Round over! Score: ] (score)) for (4) seconds
              

when I receive [clock v]
repeat until <<(timer) > (60)> or <(lives) = (0)>>
  set [time left v] to (round ((60) - (timer)))
end
              

Basic — a sixty-second round 25 min

Open your game from last lesson. Change one thing at a time, and test after each.

Step 1 — two new variables

1. Make lives and time left. Leave both ticked.
2. A space in a variable name is fine. time left reads better than tl.

Step 2 — swap the loop

1. Drag your blocks out of repeat (5) and throw the repeat away.
2. Get repeat until from Control.
3. Build <<(timer) > (60)> or <(lives) = (0)>> and drop it in the diamond.
4. Put your question blocks back inside.

Step 3 — the start of the round

1. Above the loop: set [lives v] to (3), then reset timer, then broadcast [clock v].
2. In the else half: change [lives v] by (-1).

Step 4 — the clock

1. Start a new script with when I receive [clock v].
2. Put the same repeat until inside it. Right-click the diamond and Duplicate it.
3. Inside: set [time left v] to (round ((60) - (timer))).

Step 5 — the end

1. Under the loop, say the score with a join.
2. Play one round well. Then play one getting three wrong fast.

Your two scripts should match the pair in Learnt section 6. The embed there is the finished round.

A 30-second sprint

Make the round last 30 seconds instead of 60.

• time left starts at 30.
• The round ends on its own at 30 seconds.
• Running out of lives still ends it early.

Hurry up!

Make the last ten seconds feel different, so the player knows time is short.

• With 10 seconds or less left, the Wizard changes colour.
• He says “Hurry!” while he waits.
• Before that, he looks normal.

when flag clicked
clear graphic effects
reset timer
repeat until <(timer) > (20)>
  set [time left v] to (round ((20) - (timer)))
  if <(time left) < (11)> then
    set [color v] effect to (120)
    say [Hurry!]
  end
end
clear graphic effects
say [Time's up!] for (2) seconds
            

Two endings

The player should know WHY the round ended.

• Running out of time says “Time’s up!” and the score.
• Running out of lives says “Out of lives!” and how many were right.
• Only one ending ever shows, never both.
• Every wrong answer also says how many lives are left.

if <(lives) = (0)> then
  say (join [Out of lives! You got ] (join (score) [ right.])) for (4) seconds
else
  say (join [Time's up! You scored ] (score)) for (4) seconds
end
            

say (join [It is ] (join ((a) * (b)) (join [. Lives left: ] (lives)))) for (2) seconds
            

Fast answers score double

A right answer given in under 3 seconds is worth 2 points. A slower one is worth 1.

• The Wizard says “Fast! Double points.” for a quick answer.
• Slow right answers still score 1.
• Wrong answers still cost a life, fast or slow.

set [asked at v] to (timer)
ask (join (a) (join [ × ] (b))) and wait
if <(answer) = ((a) * (b))> then
  if <((timer) - (asked at)) < (3)> then
    change [score v] by (2)
    say [Fast! Double points.] for (1) seconds
  else
    change [score v] by (1)
    say [Correct!] for (1) seconds
  end
else
  change [lives v] by (-1)
end
            

Summary 4 min

Today the game got a clock, and a way to lose.

1. (timer) counts up by itself. reset timer sends it back to 0.
2. (round ((60) - (timer))) is the time left, in whole seconds.
3. repeat until keeps going until its diamond is true.
4. <<> or <>> ends the round on time OR on lives.
5. A clock that must keep ticking gets its own script.

Timer

Scratch’s stopwatch. It counts seconds, and never stops by itself.

Round

To tidy a number to the nearest whole one. 56.7 becomes 57.

Repeat until

A loop that stops when something becomes true.

Or

True when either side is true.

Next lesson: a streak that makes right answers worth more, and an easy or hard level.