CS208, Friday 28 Jan 2022

Miscellany

• Please change your Carleton password no later than Feb 6.
• A request from me to anybody in the room who's fired up about blockchain
• One picture of Maisie, as requested by more than one of you.
  

In-class exam, Wed Feb 2

• General info
  • Closed-everything-except-your-brain
  • In Olin 304/306
  • If you have official accommodations related to test-taking conditions, I'd be grateful for a reminder before Wednesday
  • If you won't be able to attend due to COVID restrictions, let me know as soon as practical
• General topics
  • data representation
  • C
  • x86 assembly basics
• My philosophy of in-class exams
  • Stuff that I want you to have in your head, not just your notes
  • Mostly "what" and "how", only a little bit of "why"
  • No tricks
  • I try not to make it long (occasionally, I screw this up, but mostly not)
  • I indicate what I think is most important for you right now via classroom topics, homework assignments, sample programs, and quizzes
• What to study
  • homework assignments
  • quiz
  • sample code
  • class notes
  • backup reference material: textbook readings
• Types of questions
  • Short answers
  • Here's some code; what's the output?
  • Write this tiny amount of code to do X
  • That memory grid from the quiz
  • Wildcard (I reserve the right to come up with a different type of question, but see philosophy above)
• Integers
  • binary/decimal/hexadecimal notation
  • two's complement
• Characters
  • difference between characters and C char
  • codepoints vs. encodings
  • UTF-8 encoding (with chart in hand)
• C types
  • int vs. long
  • char *p vs. char p[10]
  • string literals: "Hello"
  • char literals: 'A', '\0', '\', '\''
  • sizeof (don't confuse with strlen!)
• C I/O (input/output)
  • printf, %c, %s, %d, %x, %X
  • fgets (including what if line is longer than buffer?)
• Null-terminated char strings
  • printf %s vs. %p
  • strlen
  • strcpy vs. strncpy (including what if source is longer than buffer in strncpy)
  • strcmp
• C pointers
  • & as unary "address-of" operator
  • * in type declarations
  • * as unary operator for dereferencing
  • assignment statements with pointers
• C bitwise operators
  • ~ (not)
  • & (and)
  • | (or)
  • ^ (exclusive or / xor)
• C stuff that's pretty much the same as Java
  • if, else
  • &&, ||, !
  • while, for
  • {}, ()
  • +, -, / (int div), %
  • function signatures
• Basics of x86_64 assembly
  • registers (what are they?)
  • mov, lea, add, sub, push, pop
  • test, cmp
  • j, js, jz, jl, jle
  • call, ret
  • how do you loop?
  • how do you do if/else?
  • how do you call a function?

Turning assembly back into C

• Some instructions to get straight
  • cmp, test
  • j, jl, je, jle, jz, js
  • call, ret
• Draw a picture
• Experiment with Compiler Explorer: what do simple loops, simple if/else, etc. look like?
• What can we assume about the registers at the beginning of a function?
• What does a function call look like?

Let's try puzzle0