Programming games

Drawing logo. Expressions. Formulas. Credit cards. Form validation.

Homework: your credit card program. Continue uploading work.

HTML5 logo

• http://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 formulasdistance = velocity x time

Code, assume distance, velocity, time all variablesdistance = velocity * time;

multiplication

=== checks for datatype & value

Function expressing formulafunction 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

Tempfahrenheit = Tempcentigrade*(9/5)+32;

Check by putting in points for boiling:

212 Fahrenheit and 100 CentigradeFor freezing

32 Fahrenheit and 0 CentigradeWhat 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, -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

Precedence

• Many programming courses start off with rules of precedencea*b+cIs evaluated as (a*b)+c. The multiplication is done

firstThe 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 priceLogic: 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: http://faculty.purchase.edu/jeanine.meyer/creditcard.html

Notes: http://faculty.purchase.edu/jeanine.meyer/credit.doc

Credit cards!!!!

• Calculation (as indicated by code)balance = old_balance + purchasesSubtract the payment:

balance = balance – paymentCompute interest

Divide ANNUAL interest by 12.REMEMBER DECIMAL POINTbalance = 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.

– ?????