EBoard 09: Strings (Section 1)

Warning! You are being recorded (and transcribed) (provided the technology is working correctly).

Please follow the traditional start-of-class approach.

Approximate overview

• Quiz
• Administrative stuff
• Lab

Administrative stuff

Introductory Notes

• I sent out email on Wednesday and Thursday evenings. If you did not receive that email, please let me know.
• Don’t forget to turn in reading responses! I’ve responded to all of the ones that I received on strings, but seem to be missing about 15.
• Currently, Monday’s readings don’t show the output of the Scheme functions. (Don’t ask why.) That should be fixed by the end of the day.

Upcoming activities

Scholarly

• Friday, 18 September 2026, 4:10–5:00 p.m., Noyce 3830 (ELBICA). AI Coffee Chat: Spring MAPs Today
• Tuesday, 22 September 2026, Noon–1:00 p.m., Unknown location. CS Table
• Thursday, 24 September 2026, 11:00 a.m.–noon, Herrick Chapel. Scholars’ Convocation: The Story of Our Founding: America at 250 with Annette Gordon-Reed New

Artistic/Cultural

• Any day. Visit the GCMOA for at least 30 minutes.
• Friday, 25 September 2026, 7:30–9:00 p.m., Sebring Lewis. Jazz Ensemble: Terry Riley’s “In C” New

Multicultural

• Friday, 18 September 2026, 4:10–5:00 p.m., HSSC N1170. Middle of Everywhere (Philippines) Today
• Friday, 25 September 2026, 4:10–5:00 p.m., HSSC N1170. Middle of Everywhere (Somewhere)

Peer

Musical, theatric, sporting, academic, and similar events involving this section’s students are welcome.

Wellness

• Friday, 18 September 2026, 6:30–8:00 p.m., Bear Dance Studio. Brazilian Jiu-Jitsu
• Saturday, 19 September 2026, Noon–2:00 p.m., Younker Hammocks. Picnic and Craft.
• Monday, 21 September 2026, 6:30–8:00 p.m., Bear Dance Studio. Brazilian Jiu-Jitsu
• Monday, 21 September 2026, 8:00–9:00 p.m., Prayer Garage. Meditation Group
• Tuesday, 22 September 2026, 4:30–6:00 p.m., Bear P103. Wellness Yoga
• Wednesday, 23 September 2026, 6:30–8:00 p.m., Bear Dance Studio. Brazilian Jiu-Jitsu
• Wednesday, 30 September 2026, 4:15–5:45 p.m., Undisclosed Location. Forest Bathing
• Saturday, 10 October 2026, All Day, Somewhere. Mental Health Training.
  • Sign up on Handshake.
  • It’s all day, so you will earn 3 tokens.

Misc

• Wednesday, 23 September 2026, 8:00–9:00 p.m., Science 3820. Mentor Session
• Thursday, 24 September 2026, 8:00–9:00 p.m., Science 3820. Mentor Session
• Friday, 25 September 2026, 5:00 p.m.–???, Merrill Park East. CS Picnic New

Other good things

These do not earn tokens, but are worth your consideration.

• Saturday, 19 September 2026, 8:00 a.m–4:00 p.m., Mac and Ward Fields. Grinnelleanore Roosevelts Ultimate Tournament
• Saturday, 19 September 2026, 9:00 a.m.–Noon, Tennis Courts. Women’s Tennis vs. Ripon
• Saturday, 19 September 2026, 3:00–6:00 p.m., Tennis Courts. Women’s Tennis vs. Luther

Upcoming work

• Due Sunday, 2026-09-20
  • Today’s Lab
    • Submit lab on Gradescope
    • Please submit at the end of class.
  • Readings
    • Boolean values and predicate procedures
    • Conditional values in Scheme
    • Submit reading responses on Gradescope
• On Friday, 2026-09-25:
  • New Quiz/LA on conditionals.
  • MAKEUP Quiz/LA on compose, cut, and section.
  • MAKEUP Quiz/LA on tracing
  • MAKEUP Quiz/LA on decomposition.
  • MAKEUP Quiz/LA on procedures.
• Due Tuesday, 2026-09-29
  • Mini-project 2
    • Not yet on Gradescope

Administrative Q&A

There are so many procedures in the reading. How important is it that we learn all of them?

I don’t expect you to memorize them, but you should know that “there’s a procedure that does this”, even if you can’t recall the name.

I do expect you to be able to read their use.

Don’t forget that we have flashcards (and that you have notebooks and cheat sheets).

I couldn’t make it to class Friday. Can I take the quizzes on another day?

You can take the makeups next week. One of the consequences of mastery grading is that I will generally push you to the next week rather than allowing you to make them at another time. (That also means that I can send out answers/notes more promptly.)

Friday PSA

• You are awesome, so please take care of yourselves.
• Do what is right for you, not what you think others are doing (or what others expect you to do).
• Consent is essential (but insufficient).

Questions on the readings

I will not go over these explicitly. You may want to look at them with your partner.

Why is the space character positioned at 32?

Computer scientists like powers of 2. This serves as a nice breaking point between characters that do something a bit atypical from those that print.

Why do we have to put \# in front of a character in order for char->integer to work?

The \# tell the computer to treat the character as a character, rather than, say, an identifier (variable).

Why does char-lower-case? turn characters into diffferent characters?

char-lower-case? checks whether or not a character is lowercase. It returns either true (#t) or false (#f). That will make more sense once you read Monday’s readings.

You mention there is a way to implement alphabetic to the letter characters, but how? Is it the #/a #/n #/z example that became #t?

Yes, it’s that example.

Was #f being placed in the “more character predicates” section also mean it was false?

Yes.

What do the special chars represent?

It depends on the character. The ones less than 32 often represent special information we’d use in transferring data from computer to computer or keys on old-fashioned keyboards (like “bell”).

The ones over 128 are “unamerican” characters.

Why would we need to use this code?

To build and understand functions that work with text.

I would like to request, if possible, a demonstration or more clear example on how and why you would use these functions like char<

Next week

Lab

Questions …

Use (list->string (list ...)) to build a string from a list of characters.

For example (list->string (list #\S #\a #\m #\R)) makes my name.