Overview

• Preliminaries.
  • Admin.
  • Upcoming work.
  • Questions on the HW.
• Boolean values.
• Predicates - Procedures that return Boolean values.
• Combining booleans and other values with and and or.
• Lab.

Preliminaries

Admin

• Cookies!
• It's "Pick your own partner" week.
• I apologize for the problems in MathLAN. (They are not my fault, but I do worry that they affect your ability to get work done.)
  • I have made HW 4 optional.
• I have virtual computers for 151 that you can run on your own computer.
  • Get a flash drive from Ajuna.
  • Use the file called Xubuntu151-v1.2.vba.o??, open it with VirtualBox.
  • See instructions at https://github.com/GlimmerLabs/virtual-mediascheme/blob/master/UserGuide.md
  • I'll also email a link.
• Some folks have asked me about the email posters around campus. Do you want me to give my perspective on these matters?
• Extra credit:
  • Thursday extra: Technical Interviews.
  • Friday CS Table: Skip Lists.
  • Improv Saturday, 7pm, Younker.

Upcoming Work

• Reading for Wednesday: Conditionals
• NO WRITEUP, Except for the people who failed to read this.
• Today's lab writeup: Exercises 4a, 4b, and 5
  • Subject: CSC 151.02 Writeup 13: Booleans and Predicates (OPTIONAL NAME)
• Review exam answer key.
• Sign up for a meeting if you invoked "there's more to life" (sign up sheet outside my office)

Questions on the homework?

Boolean values

What questions do we ask when we learn a new data type?

• What are they?
  • Truth!
• What do we use them for?
  • To make decisions
• What are the legal values?
  • True and false
  • In Scheme, there's false and "everything else"
• How do we express them?
  • #t
  • #f
• How does the computer display/show the data types to us?
  • #t
  • #f

Predicates - Procedures that return Boolean values

• Questions we can ask
  • Is x < 2?
  • Is this an RGB color?
  • Is this an active image?
• Some built in
• Some we write

Combining booleans and other values with and and or

and combines two (or more values)

• Gives true if all of the things are true
• Gives false if any of the things are false
• What if some are neither true nor false?
  • If all of them are trueish, it returns the last one.

or combines two (or more values)

• If any of them are truish, returns the first truish one.
• Returns #f if all of the values are false.

What do expect to get for

• (or)
• (and)

Lab