Programming games Drawing logo. Expressions. Formulas. Credit cards. Form validation. Homework: your credit card program. Continue uploading work.

HTML5 logo html5/html5logoscale.htmlhttp://faculty.purchase.edu/jeanine.meyer/ html5/html5logoscale.html Examine code Divide up code: each group explains section.

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

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.

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?

Caution Recall: Programming systems store whole numbers (0, 1, 2, -10, etc.) differently than numbers with fractions (0.5, 10.23, , 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

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

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 =.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!

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; }

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

A man walks into a bar… See also: creditcard.html creditcard.html Notes: credit.doc credit.doc

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

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)

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.

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!

Describe 3 mistakes in the following code for calculating days in the month switch(mon { case “Sep”: case “Apr”: case “Jun”: case “Nov”: daysInMonth = “This month has 30 days.”; case “Feb”: daysInMonth = “This month has 28 days.”; break; default: daysInMonth = “This month has 31 days.”; }

Classwork/homework Prepare your own [simplified] credit card calculator Do something original –use pictures. –Look up how to specify input to be numbers and within limits and use this for the input fields. –?????