CS3: Introduction to Symbolic ProgrammingSpring 2006 Nate [email protected] 3:ReviewCase StudiesAnnouncements•Nate's office hours:-Wednesday, 1:30-3:30-329 Soda•Tue/Wed is a Catch-up day.-Use this day to catch up! That is, go back over the last two weeks and fill in places you missed-You will all be ready to go on Thur/Fri, right?•We are still waiting on readers for homework grading…ScheduleLecture: Midterm 1 Lab: Recursion IIOct 2-66Lecture: Introduction to RecursionLab: RecursionSep 25-295Lecture: Data abstraction in DbDLab: Miniproject ISep 18-224Lecture: Case StudiesReading: Difference between Dates (just the first version in the reader)Lab: Work with Difference between DatesSep 11-153Lecture: <holiday>Lab: Conditionals, Booleans, TestingSep 4-82ReviewWhat is Scheme? -A easy yet powerful programming language-The "Listener" makes testing easy-Unique features like "quoting"•Words and sentences-Not usually part of scheme, but makes our early work more accessible•Quoting something means treating it literally:-you are interested in the name that follows, rather than what is named-Quoting is a shortcut to putting literal things right in your code. As your programs get bigger, you will do this less and less.Some terminology•Conditional-cond and if•Booleans-#t and #f-in practice, everything is true except #ffalse is true! (really, false is #t)•Predicates-procedures that return #t or #f-by convention, their names end with a "?"(odd? 5) ➨ #t(member? 'x '(a e i o u)) ➨ #fReview: testing•There is much more to programming than writing code-Testing is crucial, and an emphasis of this course-Analysis-Debugging-Maintenance. -"Design"Some nice comments•"In English, when something is in quotes we think about it differently. Same in scheme"•"In order to remember how to parenthesize a cond statement... think of each statement as an if without the 'if' " (actually, in lecture I mentioned that these quotes came from you guys, but I was wrong: these came from an earlier semester Still, your quotes were just as good, I just used the wrong slide...)A video resource•http://wla.berkeley.eduWeiner lecture archives•The "course" is an earlier CS3-Different emphasis; early lectures may work better than later ones-Very different lab experience-Same bookWrite an answer procedure. Write a procedure named answer that, given a sentence that represents a question, returns a simple answer to that question. (A question's last word ends with a question mark.) If the argument sentence is not a question, answer should merely return the argument unchanged. -Given ( am i ...? ), answer should return ( you are ...). -Given ( are you ...? ), answer should return ( i am ...). -Given ( some-other-word i ... ? ), answer should return ( you some-other-word ...). -Given ( some-other-word you ... ? ), answer should return ( i some-other-word ...). -Given any other question, answer should return the result of replacing the question mark by a period.You are writing big programs now. But, what can’t you do yet?What does “understand a program” mean?A big idea•Data abstraction-Constructors: procedures to make a piece of data-word and sentence-Selectors: procedures to return parts of that data piece-first, butfirst, etc.Case Studies•Reading!?•A case study:-starts with a problem statement-ends with a solution-in between, a …story… (narrative)-How a program comes to be•You will write “day-span”, which calculates the number of days between two dates in a yearYou need to read this•The lab will cover the case study through a variety of activities.-This will culminate in the first “mini-project”•We just may base exam questions on it•It will make you a better programmer! 4 out of 5 educational researchers say so.Some important points•There is a large "dead-end" in this text-Like occur in many programming projects-Good "style" helps minimize the impacts of these•There is (often) a difference between good algorithms and between human thinkingExtra Materials(define (walk light city cops-present) (cond ((equal? city 'berkeley) 'strut) ((equal? light 'green) 'go) ((equal? light 'not-working) 'go-if-clear) ((and (equal? light 'flashing-red) cops-present) 'wait) ((equal? light 'flashing-red) 'hurry) (else