CSC 110 - Intro. to Computing

1. CSC 110 -Intro. to Computing Lecture 17: Even More Robotran!

2. Announcements • Quiz #4 will given out at end of class on Thursday • Covers Palgo and Robotran • But not Robocop, since I never saw it.  • Homework Solutions available on web page • Thursday also marks a return to the book • We will be discussing operating systems

3. Subprograms & Functions & Handlers, Oh My! • Often there is code we want to execute repeatedly, but not in a loop • Drawing the sides of a box • Writing each line in the letter “B” • Performing the Open… window • Turning robot around whenever “RUN” button pushed • Want to do this without having to rewrite code everywhere.

4. Subprograms • Subprograms begin with a valid name • Any letter combination EXCEPT the program name and reserved words are legal • We will use this, so use a meaningful name • drawSquare better than pollyWantACracker • Robotran subprograms begin and end similarly: define nameThe subprogram code goes hereend

5. Simple Subprogram program example1 for s = 1 to 4 do drawLineend define drawLine pen down go forward 1 inch turn sharp right pen upend

6. More Complex Subprogram • What if we want the lines to be different sizes? • Parameters allow us to pass values to a subprogram • Creates new variable(s) at subprogram start and assigns this variable the supplied value • Cannot use the parameters outside the subprogram

7. Working With Parameters program squares do drawSquare(0.7) go forward 0.1 inch do drawSqare(0.4) define drawSquare(parm length) pen down repeat 4 times go forward length inches turn sharp right end pen up end

8. Functions • Sometimes subprograms should compute a value • Like Excel’s max(), min(), average(), etc. • Subprograms return 1 value at a time • These subprograms called “functions” • This happens a lot in the real world… • …but I lack a good classroom example. • Please bear with me!

9. Function Example program walker var distance var angle while true do let distance = getRand(3) go forward distance inches let angle = getRand(360) turn right angle degrees end define getRand (parm max) returns float var number = random/100.0 * max return number end

10. Event Handlers • Some things in life you can predict: • Death • Taxes • Politicians making impossible promises • People upset at politicians breaking promises • Cubs not winning the World Series • For everything else there are Event Handlers™

11. Robotran Event Handlers • These are subroutines that are run only when you hit a button • Event handlers cannot use parameters • Remember, cannot be called like subroutines

12. Button Handler program handler go forward continue when RUN button is pressed var angle = random + 90 turn left angle degrees end when VIEW button is pressed var angle = random + 90 turn right angle degrees end

13. A Toy My Daughter Would Love program Shoshanna global var count = 0 go forward continue when RUN button is pressed let count = count + 1 stop turn left random degrees end when VIEW button is pressed beep end when PRGM button is pressed display count end

14. Your Turn • Write program so your robot moves forward until it hits something. When it hits something it should stop and beep. • Add event handlers so that when the RUN or PRGM button is hit your robot turns around 180 degrees and resumes going forward. • Add a global variable which is set to 1 whenever the RUN button is pressed and set to 2 whenever the PRGM button is pressed. • Whenever you hit something, display the number of the player who gets a point (e.g., the last player to hit their button) and then turn around and restart going forward.

15. For Next Lecture • Read chapter 10 in the book • Study for the Quiz #4