Unit 5 Seminar 1

7/25/2019 Unit 5 Seminar 1

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Randomization and Variables


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Random Numbers

When programminggames, we often wantto use random

numbers

Scratch providesbuilt-in functions for

generating randomnumbers.


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Catch ames

!ou need to use random numbers in catch games

Scenario" # bunches of bananas are followingfrom the s$% and the user is to use the arrow $e%

to move a mouse to catch them&n order to record scores, we need to use avariable ' we will use it in this program ande(plain later.


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)lgorithm

*. +on$e% prompts user what to do. Set mon$e%s initial position

. /et user move mon$e% with arrow $e%

0. Set score to 1

#. /oop # times2ut banana in a random position

Show and let banana fall down

&f banana meets mon$e%

score 3 score 4*

5ide banana

6. ame 7ver


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bananaScript 8*9

!ou should beable to write themon$e%Script%ourself. 5ereshow %ou write themain program of

the bananaScript


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bananaScript 89

Notice %ou onl% needto randomize (. &talwa%s falls from thes$%

&t needs to fall straight

down ' use the samenumber for (


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Write %our own game

!ou will be as$ed to write %our owncatch game. Remember to add aprompt before the game starts andgame over when it ends.

)t this point %ou are initializing the

score in the bananaScript. &t will bemodified later after %ou learn moreabout the scope of variables


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5aunted Castle

Can %ou write a program of a ghost is appearingand disappearing in different spots in a castle:


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+ove Sprite to Random 2osition

2ut the randomizednumber in the appropriatebo(

We use *01 and 11 andnot the whole stage toaccommodate the size of

the spriteWrite the program andsave it as ;haunted< ' we

need to modif% it later


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Score

=he program can easil% be turned to agame b% letting the user clic$ on theghost.

=o record score, we need to use variables' we have alread% done so before but letsloo$ at it closel% before continuing with thegame.


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Variables

) variable is a named storage location inthe computers memor%

) variable can onl% hold onevalue at atime. ) new value will replace the previous

one


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Scope

=he scopeof variable refers to the part of acomputer where a variable is binding

/ocal variable" belongs to a specific spriteor method

lobal variable" belongs to and can beused in the whole program


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Variable Name and &nitial Value

Variable Names"+ust be uni>uewithin the method ' can be casesensitive depending on the language

Should be meaningful

&nitial Value"=he value that is first stored in the variable whenit is created. &nitializingmeans setting a value for

a variable when it is first created.&n Scratch %ou must initialize as it $eeps thevalue of the variables of the previous run of theprogram


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Counting Numbers

?se data to create a localvariable to let the cat use theloop to count from * to #.


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5aunted ame

Now modif% the;haunted< program b%adding a globalvariablefor score.

!ou should be able tocount the score now


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=esting and @i(ing Augs

=he program seemsto wor$ well 'however, if %ou hit the

same ghost twice oreven thrice, the scorecontinues to add up.

=he wa% to fi( it is tochec$ whether theghost has alread% been

clic$ed each time itappears. &f it is the firsttime, add score,otherwise, no score

)lso, the game never ends. !oushould add a global variable to set atime limit for the game to end


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)lgorithm for @irst 2erson Shootingame

;5aunted< is a first person shooting8ffs9 game. /ets doit properl% again starting from the algorithm"

*.Set all variables to 1 and time/eft to *1.Set up ghost and gives instruction

./oop @orevertime/eft 3 time/eft -*ma$e ghost disappearset isClic$ed to 1

ma$e ghost appear in a random place0.When ghost is clic$ed

&f isClic$ed is 1)dd score and effectSet isClic$ed to *

@or interactive games, %ou

should alwa%s provideinstructions or tell userwhen or how to inputinformation ' this is calleda prompt

#. &f time/eft 3 1Stop ever%thing


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bac$dropScript" lobal Variables

Remember we useglobal variables forscore and timer becausethe% are for all sprites -

in case %ou add othersprites 8e.g a witch9 thescore still wor$s

Convention" We set andif possible deal withglobal variables in thebac$dropScript


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Script for the ghostSprite

)dd comment"Calculate scores andadd effect

+odif% and save;haunted< again.


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Codes for the +ethods


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)ccumulator

=he score increases b% * each time, but%ou can also decide how much to increase

)n accumulatoris a variable used tocalculate the total of some numbers

&magine %ou have a new pigg% ban$. =hefirst time %ou put in B. =he second timeB*. =he third time B0. 5ow much is therein the pigg% ban$:


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)lgorithm

*st time" =otal 3 =otal 4 8 1 4 3 9

nd time" =otal 3 =otal 4 * 8 4 * 3 9

rd time" =otal 3 =otal 4 0 8 4 0 3 9)s a result, %ou have B in %our ban$.

=he algorithm is"

Total = Total + Amount Each Time


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Cashier

We will write a program to demonstratethis.

=here are a few items with prices. =heuser is going to clic$ on the item and thetotal amount will be calculated.


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)dd the Sprites

!ou need a cashier and some fruits. )ddprices to fruits and ma$e a chec$ out sprite


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)lgorithm

*. +a$e three global variables ' current price, ta(and total price and initialize them to zero

. Dach time an item is clic$ed"

current price 3 item pricetotal 3 total 4 current price

0. When chec$ out is clic$ed"

ta( 3 total E 1.*total 3 total 4 ta(

Cashier sa%s the total


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=he Code" &nitialization andCalculate one item 8*9


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=he Code" 7ther &tems 89

)s all the other items calculate the samewa%, clic$ and drag the appleScript to the

other fruits and change the current price tothe corresponding price


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=he Code" chec$7ut 89

When the user clic$s the chec$7ut sprite, itneeds to send a message to the cashier so shewill do the calculation. !ou have alread%

learned how to use it in ?nit 0 ' use broadcast.


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=he Code 809 " cashierScript

Save theprogramas;cashier

Documents

Unit 5 Seminar 1