Week 2 · Tuesday, Jan 12 · 2.2
Casting and limits
A cast changes a value's type: (int) cuts off the decimal part and (double) turns an int into a double, and every number type has limits on how big and how exact it can be.
Minutes for each part of a 90-minute class.
Today we will
- A cast puts a type in parentheses before a value: (double) 7 is 7.0, and (int) 9.87 is 9.
- (int) truncates: it cuts off the decimal part. It does not round.
- A cast applies to the value right after it, so (double) 7 / 2 is 3.5 but (double) (7 / 2) is 3.0.
- To round a double that is not negative, add 0.5 and then cast: (int) (x + 0.5).
- An int has a smallest and largest value, Integer.MIN_VALUE and Integer.MAX_VALUE. Going past them is integer overflow.
- A double is stored in a limited amount of memory, so some results are slightly off. That is round-off error.
Terms
AP topics 1.5 · Learning objectives 1.5.A, 1.5.B, 1.5.C · Skills 2.A, 3.A, 4.A
Demonstration
Chromebooks open. Follow along on the Follow along jobs in We Do / You Do while Mr. Muggivan works the examples.
We Do / You Do
Follow along, then Part A (with help), Part B (on your own) and stretch. One code for the whole block.
Open We Do / You DoExit Ticket
A few exam-style items to show what you learned today. One code.
Opens only in the last 15 minutes of class on this day.
Missed class? The Do Now and We Do / You Do stay open. Do them any time and submit your codes.