CSC151.01 2015F, Class 03: An Introduction to Scheme ==================================================== _Overview_ * Preliminaries. * Admin. * Upcoming Work. * Extra Credit. * Questions. * Lab! * Debrief. Preliminaries ------------- ### Admin * Apologies about occasional lab confusion yesterday. * You now know how to get online, so I won't be providing printed copies of the lab manuals. * My normal office hours are MWF 11:00-11:50. You sign up for those at . I will also schedule meetings in other times. My paperwork times are probably the best, M-F, 8-9 am. Check my schedule for more. (I'll give up the occasional class prep time if necessary, but I prefer advance notice.) * The mentors will be surveying you about preferred time for mentor sessions (probably Wednesday and Thursday evenings) ### Upcoming Work * Two readings for Wednesday: [Numeric Values](../readings/numbers-reading.html) and [Symbolic Values](../readings/symbols-reading.html) * HW 2 to be distributed tomorrow. * Quiz 1 on Friday. ### Extra Credit Opportunities #### Academic * TODAY, noon, CS Table, JRC 224C. How Google Can Manipulate Elections. Readings available in the back of the classroom. If you are not on a meal plan, we'll pay for your meal. #### Peer Support * Pals of PALS, pals@grinnell.edu, normally Saturday at 1:30 and Mondays at 4:45. Requires sign up in advance. * Pun Club, Saturdays, 4pm, Way over Younker ### Leftover Questions on Algorithms **Thanks very much to the students who provided these questions!** _Can you give an example of a subroutine from the nut butter and preserve algorithm?_ > Sure. There was an "open a jar" algorithm that I could have applied to both the nut butter jar and the preserve jar. Given that the preserve jar is glass, I don't think it would have been a good idea to use the "hit the top of the jar on the counter" algorithm. Here's an alternative. (Yes, you can probably find flaws.) > To open a jar > 1. grasp the body of the jar with your non-dominant hand holding the top of the jar upward. > 2. grasp the lid of the jar with your dominant hand > 3. if the jar appears to be a screw-top jar, rotate the lid of the jar counter-clockwise while continuing to hold the bottom steady. Keep rotating the lid counter-clockwise until it separates from the jar. > 4. if the jar appears to be a pop-top jar, pull the lid upward, applying force at the edge of the lid while holding the body of the jar steady > 5. if the jar appears to be neither a screw-top jar nor a pop-top jar, report an inability to open the jar and stop. _Can you give examples of the where parts of an algorithm appear in the nut butter and preserve algorithm?_ * "Untwist" and "grab" are *basic operations*. (Many of you assumed that "open" is a basic operation. But it didn't seem to be.) * The jars, utensils, bread, plates, and napkins are the *parameters* to the algorithm. * Similarly, the jar is the *parameter* to the "open a jar" algorithm. * Within the broader algorithm, "the slices of bread" (meaning the ones that I removed from the bag) are *variables*. * Similarly, the "dominant hand" is a *variable* within the "open a jar" algorithm. * Opening the bag of bread before removing the bread is an example of *sequencing* * Questions about the type of jar are examples of *conditionals* * "Keep rotating the lid counter-clockwise until it separates from the jar" is an example of *repetition*. * And as we just saw, the "open a jar" steps are a *subroutine*. ### Additional Questions _What is the difference between basic values and parameters?_ > Parameters name the inputs to the algorithms. "jar of fruit-based substance" > Basic values are the kinds of values we can provide, such as "jar of Smuckers(r) raspberry preserves" > In math, we think about things like f(x). x is a parameter to the function f. Numbers, like 42, are basic values. Lab --- _Why can't I use `square`?_ > `square` is not defined by default in DrRacket. That was a trick to help you remember that not every natural operation is defined. (Don't worry, we'll define it soon.) _What are the shortcuts that Erin, Zachary, and Sam provided to folks?_ > In the interactions pane, control-uparrow brings back the previous command for you to edit > If you select with the left mouse button, you can (usually) paste with the middle mouse button. Debrief ------- _Where can I do work for this class?_ > For the first few weeks of class, please work on Noyce 3rd. > After that, we will provide a few additional options > 1. Use a virtual machine. > 2. Connect from your computer to ours. (Harder, sometimes slower, but gives the same files.) > 3. If you run Linux, you can install the class software (I think). > But working on Noyce 3rd is always good. _Do we need to define something before we use it?_ > Yes, in general. _How did you know that the square root was correct?_ Lab Writeup ----------- Email an answer to the following question to rebelsky@grinnell.edu. _What did you see as the learning outcomes for exercise 3_? Due Friday. Submit as a joint assignment by sending an email with all of your names.. Subject: CSC 151 Lab Writeup Day 3 (Z. Livingston Seagull and E. Gotshot) _Please substitute your own names._