Unit 2 Lab 1: Games, Page 2

You'll want the computer to ask players to guess again and again until they guess correctly. To do that, you will use the

block. Repeat until is a loop (just like repeat, forever, and for) but also a conditional (like if and if else). It repeats until a certain condition is met. For this program, the code should repeat until the player's answer equals the secret number.

Use repeat until to ask the player () to guess the secret number until their equals the secret number.

Drag the secret number variable out of the script variables block to use it.
The ask and answer blocks go together. If you use ask to ask a question, the user's answer will be reported by answer.

The code

ask (Why did the chicken cross the road?) and wait; set (user response) to (answer)

would be written as

DISPLAY("Why did the chicken cross the road?")
userResponse ← INPUT()

a white rounded rectangle containing two smaller white rounded rectangles: The first one contains first the word 'DISPLAY' in all caps and then a smaller white rectangle containing the quoted text 'Why did the chicken cross the road?'. The second one contains the text 'userResponse ← INPUT()'

AAP-3.A.8, AAP-3.A.9

Notice that the procedure

INPUT()

accepts the value from the user and returns that input value, which is then assigned to the variable

userResponse

with the

←

syntax. In Snap!, this is just like how answer accepts a value from the user and reports it, and that report is what the computer sets the variable user response to.

AAP-2.B

After the player guesses the secret number, make the computer congratulate the player.
Test and debug. Take turns playing the game, and fix any problems with the code before moving on.

Repeat until makes its decision based on the output of a hexagonal predicate block.

: Predicate and Boolean value

Why is Boolean capitalized?

The word Boolean is capitalized because it's named after a person, George Boole, who invented the branch of mathematics dealing with Boolean operations (such as and, or, and not).

A predicate is a hexagon-shaped reporter that asks a true/false question such as these examples:
8 > 7 reporting true 6 > 7 reporting false

AAP-2.E.1

Predicates report a Boolean value (either true or false ).

Predicates fit into a hexagonal input slots of conditionals, such as in if block

and

. Predicates help conditionals decide when to do something.

We really shouldn't be encouraging students to mutate a block's inputs. There are really two issues here; one is with the x=x+1 style of programming altogether, and the second is that formal parameters specifically shouldn't generally be mutated; it's better to make a script variable that's initialized to the input value. (If we change this, we need to update the Guided Notes.) --MF, 6/26/21 with BH
Which inputs to mystery function will report "finished"?

Any integer

Correct! No matter what the input number is (as long as it's an integer), the report block will eventually run. (This doesn't necessarily happen in every procedure, but here it will.)

Only integers greater than or equal to 5

Write out some examples of what happens when the input is less than 5. For example, if the input is 3, the sprite will say 3, the input will be changed to 4, the sprite will say 4, the input will be changed to 5, the repeat until loop will stop, and the function will report "finished."

Only integers less than 5

The report command isn't inside the if.

Only 5

The repeat until block checks the value of input every time through the loop, not just its initial value.
What will the sprite say if you run the same function with the input 1?

It does say 4 at the end, but it says other things before that.

How does repeat until work?

Correct! The repeat until block runs the code in its script slot until input = 5, then the computer skips down to the next command, report (finished), without the sprite ever saying 5.

The repeat until block tests the value of input before running the code in its script slot.

The feedback is not finished because I realized that BH might object to changing the value of an input variable... --MF, 3/1/19
What will happen if you run the same function with the input 9?

The sprite will say 9, and the block will report "finished."

What does the if block do when input is 9?

The sprite will say 9, 8, 7, 6, and the block will report "finished."

What does the set instruction do to the value of input?

The sprite will say 9, 10, 11, 12, 13, … and keep counting, and the block will never report "finished."

When input is 9, will the code inside the if command run?

The sprite will say nothing, and the block will report "finished."

Correct! The code inside the if command will not run.

The feedback is not finished because I realized that BH might object to changing the value of an input variable... --MF, 3/1/19

Checking the Player's Guess