Programming Games

1
Programming Games

• Formulas. Date. Representation in computer
  Storage. Credit Card.
• Homework Finish slide show.Upload application

2
Overview

• Representation of information. How is
  everything/anything represented 'in' the computer
• Storage
• Formulas
• Simplified credit card calculation

3
Storage

• Everything (data and programs) is stored in the
  circuitry of 'the computer'.
• The circuitry includes transistors that are
  switches on or off states, 0 or 1. Each switch
  is called a bit.
• So.numbers are stored using the binary (base 2)
  system
• Symbols (characters, letters, etc.) are stored
  using agreed upon systems of encoding
• ASCII 8 bits per character
• UNICODE 16 bits per character

4
Why?

• Why not use circuits that can more easily
  represent numbers using the decimal (base 10)
  system?
• Answer Easier to make on/off switches than
  something with 10 states. Easier to build
  circuitry for calculations for the base 2
  addition and base 2 times tables than the ones
  you remember

5
Recall base 10

• Recall 1s column, 10s column, 100s column
• Recall borrowing (re-grouping) and carrying
• Do problem(s)

6
Base 2

• Same principle
• 1s column, 2s column, 4s column, ????
• Do problem(s)

7
Joke

• Explain joke on shirt

8
Base 16

• Hexadecimal used for quick way to describe bits,
  mostly commonly for color coding
• Symbols used are 0, 1, 2, , 9, A, B, C, D, E, F
• You may have seen color coding RGB (red, green
  blue) FF0000 is red 00FF00 is green ??

9
Numbers with fraction part

• Aka numbers with a decimal point
• How to represent?
• ANSWER floating point numbersaka scientific
  notation
• 3.4521 102 is the same as 345.21 100
• Terminology 3.4521 (or 345.21) is the mantissa
  or significand and the 2 (or 0) is the exponent.
• Computer format use 2 or 16 in place of 10
• Example using 32 bits
• 1 bit for the sign (0 for , 1 for -)
• 8 bits for the exponent
• 23 bits for the mantissa (width, i.e., 23, is the
  precision)

10
Characters

• ASCII coding
• The character A is represented by 01000001
• The character a is represented by 01100001
• The character 1 is represented by 00110001
• The character 2 is represented by 00110010
• .
• Unicode is a 16 bit format big enough (hopefully)
  for all the world's languages

11
String of characters

• such as a name or a label or a piece of text
• Fixed length allocate 1 byte (8 bits) for each
  character
• UNICODE 2 bytes
• Variable length store string in two parts
• One part holds length as a number and pointer
  (address) of the whole string
• String itself

12
Boolean

• Named after George Boole
• True / False
• Theoretically 1 bit, 0 for false, 1 for true but
• The addressability requirement means it could be
  1 byte or even bigger
• String of Booleans can be combined.
• A byte can represent the answer to 8 true/false
  questions.

13
Other information

• Programming generally requires encoding of
  information.
• The encoding CAN BE arbitrary, but does need to
  be defined
• Later My rock paper scissors game assigns 0 to
  rock, 1 to paper and 2 to scissors. The player
  NEVER sees this.
• Many systems of encodings start with 0
• Arrays (sets of values) are indexed starting with
  0.

14
Aside

• Representation somewhat analogous to issue of
  units?
• Some number represents measurement of length or
  distance or displacement or size. What unit?
• Numbers by themselves rarely convey information
• Compared to what?
• Out of what?
• Definition, Denominator, Distribution, Difference

15
Instructions

• Computer storage holds
• Instructions (the code)
• Instructions may be translation (compilation) of
  higher level instructions
• Machine code Load Register, Store Register, Add,
  Multiply, Check value and jump, etc.
• Information
• Can't look at the bits and say what it is
• 01001010 the letter J or the number 74 or ...

16
Reflect and Continue

• Storage of standard things (e.g., numbers) solved
  but representation of information for specific
  problems is / will be new challenge
• Now on to representation of formulas and logic.
• Closed form mathematical formula easy to
  represent in code
• Algorithm, logic, may require use of
  conditionals, more
• Models build computer model representation of
  something, some phenomenon. NOT simple (closed
  form) formula, but involving programs

17
Formulas

• Programming languages have features for
  expressing mathematical formulas
• distance velocity x time
• Code, assume distance, velocity, time all
  variables
• distance velocity time

multiplication
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Function expressing formula

• function distance (velocity, time
• return velocity time
• Give me velocity and time and I'll the function
  will return the distance.
• The function header indicates the incoming
  parameters (aka arguments). NOTE in ActionScript
  and some other languages, the function header
  also indicates datatypes of the parameters and
  the returned value.

19
Temperature conversion

• Tempfahrenheit Tempcentigrade(9/5)32
• Check by putting in points
• for boiling
• 212 Fahrenheit and 100 Centigrade
• For freezing
• 32 Fahrenheit and 0 Centigrade
• What is formula for the other direction?

20
Caution

• Recall Programming systems store whole numbers
  (0, 1, 2, -10, etc.) differently than numbers
  with fractions (0.5, 10.23, -2.3333333, etc.)
• Need to make sure that none of the intermediate
  steps are truncated to whole numbers!
• One approach write 9.0 and 5.0 and 32.0
• Note problem occurs with the division, not
  multiplication or addition

21
Precedence

• Many programming courses start off with rules of
  precedenceabc
• Is evaluated as (ab)c. The multiplication is
  done first
• Recommendation put in parentheses!
• MAYBE avoid long statementsuse multiple lines

22
Conditionals

• Suppose a formula (for ticket price or score or
  ) involves a conditional test
• One Tuesdays, drinks are half price
• Logic if it is Tuesday, dcost .5dcost
• Implementation use if statement
• Alternative conditional operator. Show later.
• But how do we know if it is Tuesday?
• Implementation use Date
• Remember from first HTML example!

23
Date code

• today new Date()
• dayofweek today.getDay()
• //encoding is 0 for Sunday, 1 for Mon.,
• // 2 for Tuesday
• if (dayofweek2)
• dcost .5 dcost

24
Conditional operator

• Operator with 3 operands condition ?
  value_if_true value_if_false
• dcost (dayofweek2) ? (.5dcost) dcost
• Comfortable_with_conditional ? Use_It
  if_statement

25
Credit card Simplified

• Make purchases
• Receive monthly bill
• If you pay up (do NOT have a balance), no credit
  charges
• If you do not pay anything, fee interest
• If you pay the minimum, interest
• Next month, balance is remaining balance, fee,
  interest, new purchases
• Demonstrate

26
Credit card

• Multiple purchases
• Do not 'get the float' if you don't pay up
• Compounding may be DAILY
• Advice pay upnever have a balance
• Read the small print

27
Problems

• Slide show
• There is one ltimggt element. Its src is changed,
  producing the slide show.
• The code is in the ltscriptgt element. This
  includes 3 function definitions startss, stopss,
  change. The change function changes the sn
  variable (the pointer into the slides array) and
  changes the src of the img element, displaying a
  new picture.
• The ltbodygt element has the buttons, made using
  ltagt elements and the ltimggt element. You can put
  in other stuff into the ltbodygt

28
File structure on server

• You may have an index.html file for each folder,
  including the WEB folder
• If you have an html file in Folder A, and have a
  folder named pictures in folder A containing a
  file named bird.gif, the html file can refer to
  "pictures/bird.gif"

29
Scaling up

• making an application bigger / big enough after
  testing a smaller version
• The slide show can be scaled up to hold more
  slides by adding names to the array
• Note the code refers to slides.length
• Scaling up can be more difficult

30
Virtual Dog

• Discrete event simulation Model of a phenomenon
• My model of a dog's behavior
• Represent (keep track of) dog's state
• Weight, divided into ranges for purposes of the
  display
• Time since last feeding
• Player actions
• Feed
• Pet
• Stochastic (probalistic) effect

31
Your virtual something

• Start out with small number of states (pictures)
  and
• 2 actions by the player
• You may build on this application for your final
  project.
• This scaling up may be / will be more complex
  since you will be adding more conditions and
  buttons

32
Homework

• Review (will be on the midterm!)
• Binary, hexadecimal, ASCII
• Credit card application
• Finish slide show
• Upload application(s)
• Make index.html file
• Look ahead virtual something
• Plan first (states, pictures, player moves)