1. Programming Games Credit cards. Forms. Homework: Catch up: dice game. Produce your own credit card application or something else making use of a form with computations.

2. Formulas Mathematical expressions are combinations of operators and terms –examples of operators: +, -, *, /, ==, ===, !=, &&, … –examples of terms: variable name, constant Programming languages have features for expressing mathematical formulas distance = velocity x time Code, assume distance, velocity, time all variables distance = velocity * time; multiplication === checks for datatype & value

3. Well-formed expression Show a NOT well-formed expression A = B * toss(a, b, c

4. 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 many languages, the function header also indicates the datatype of each parameter and the datatype of the returned value. This makes it possible to check that the programmer is NOT using the functions incorrectly…at least as far as datatype.

5. Expressions An expression is a combination of operators and terms, with the terms being variables or literals (for example, numbers) Examples: 10 * score bill + bill*.08 now <= then + duration (day != "Saturday") ? 2200 : 2400 xpos > xborder (xpos > leftwall) && (xpos <rightwall) Note: && is logical AND operator WHICH does NOT evaluate the second term if the first is false. (gpa >3.0) || (credits >90) Note: || is logical OR operator which does NOT evaluate the second term if the first one is true.

6. Temperature conversion Temp fahrenheit = Temp centigrade *(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?

7. Interlude: Computer jargon A bit is a 1 or 0. Abbreviation b A byte is made up of 8 bits. Abbreviation B. –ASCII is a system for representing symbols, such as the letters, in 8 bits, which is 1 byte. –Unicode uses 16 bits. How many different patterns of 1s and 0s can be held in 4 bits? 8 bits? 16 bits? –Hint: start with 1 bit and keep going and notice the pattern.

8. Caution Recall: Programming systems may 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: problems occurs with the division, not multiplication or addition Extra credit opportunity: what does JavaScript do?

9. JavaScript program function convertToFahrenheit(T) { var ans; ans = (9.0/5.0) * T + 32.0; return ans; } OR function convertToFahrenheit(T) { return (9.0/5.0) * T + 32.0; }

10. Precedence Many programming courses start off with rules of precedence a*b+c Is evaluated as (a*b)+c. The multiplication is done first The alternative is a* (b+c) Recommendation: put in parentheses! MAYBE: avoid long statements—use multiple lines

11. Conditionals Suppose a formula (for ticket price or score or …) involves a conditional test: –On Tuesdays, drinks are half price Logic: if it is Tuesday, dcost =.5*dcost; 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!

12. Date code Suppose policy of half-price on Tuesdays today = new Date(); dayofweek = today.getDay(); //encoding is 0 for Sunday, 1 for Mon., // 2 for Tuesday if (dayofweek==2) { dcost =.5 * dcost; }

13. Conditional operator Operator with 3 operands condition ? value_if_true : value_if_false … dcost = (dayofweek==2) ? (.5*dcost) : dcost; Comfortable_with_conditional ? Use_It : if_statement

14. A man walks into a bar… See also: http://faculty.purchase.edu/jeanine.meyer/ creditcard.html http://faculty.purchase.edu/jeanine.meyer/ creditcard.html Notes: http://faculty.purchase.edu/jeanine.meyer/ credit.doc http://faculty.purchase.edu/jeanine.meyer/ credit.doc

15. Credit cards!!!! Calculation (as indicated by code) balance = old_balance + purchases Subtract the payment: balance = balance – payment Compute interest Divide ANNUAL interest by 12. REMEMBER DECIMAL POINT balance = balance + (balance * interest) Add fee if required: balance = balance + fee

16. Estimating 24% ANNUAL interest is 2% per month –24/12 is 2! What is 2% of $50? –2% of 100 is 2. So…2% of 50 would be 1 –What is 10% of 50? 5, so 2% would be less than that 15% ANNUAL interest. Monthly would be…more than 1 less than 2 (1.25)

17. Compounding The interest is added to what you owe. The new balance is what you haven't paid plus the interest on what you haven't paid. Next month, you will be paying interest on the interest. This doesn't include fees for not paying the minimum My program does not do compounding on a daily basis. Actual rules mean you pay more! NOTE: it still is a free loan if you pay off balance. –There are charges to merchants.

18. Compounding is your friend, when you are saving (or investing) –You earn interest and then interest on the interest. is your enemy if you owe money Interests are very low now, but they (probably) will rise!

19. Writing on image http://faculty.purchase.edu/jeanine.meyer/ html5/addmessage.htmlhttp://faculty.purchase.edu/jeanine.meyer/ html5/addmessage.html Notice different types of input –Radio buttons –Range –Color –html

20. Braiding http://faculty.purchase.edu/jeanine.meyer/ braidloosetightshake.htmlhttp://faculty.purchase.edu/jeanine.meyer/ braidloosetightshake.html Again, notice different forms of input Aside: uses 2 ½ D technique of small canvas elements (more on this later)

21. What went wrong & why? test function addone () { document.f.score.value = 1+document.f.score.value; return false; } Score:

22. Number theory examples http://faculty.purchase.edu/jeanine.meyer/ numbertheory/http://faculty.purchase.edu/jeanine.meyer/ numbertheory/

23. Hints For slide show (and any other application (program) with media,) you need to upload the image files along with the html file(s) One second for me is –One Mississippi Think about your player/customer/user… –What is expectation on controls, aka affordances

24. Recap today “Same deal” meant owe interest on everything owed. This included (original) interest + fee. JavaScript forms support text input plus URL,color, radio, other –Look it up! JavaScript also provides way to get input from user/player/customer clicking on canvas and code determines position –Code did a rotation for writing text on canvas.

25. Homework Take the credit card application and make it your own –add graphics? –change form? –? OR create another application making use of input from a form and doing calculations

26. Recap Catchup: if behind, do dice game and slide show. We will start on virtual something next week. Keep up with taking notes, doing research –Form input –How to get time of day from Date object –JavaScript way of storing numbers –Ideas for projects Get help: office hours, Einstein’s Corner