CS208 Introduction to Computer Systems
Monday, 2 October 2023

+ Let's do the quiz together

    char buffer[100];
    strcpy(buffer, "rhinoceros");
    char *p = buffer;

    1. strlen(p)                     [10]
    2. sizeof(p)                     [8]

    See spreadsheet

    3. printf("%s", s1);             [CS208marmot]
    4. printf("%d", k);              [-42]
    5. printf("%p", &k);             [0x40]
    6. printf("%p", pointers[1]);    [0x5]
    7. printf("%s", pointers[2]);    [kat]
    8. printf("%c", *pointers[0]);   [b]

========
#include <stdio.h>
  
int main() {
    int k = -42;
    char *address_of_k = (char *)&k;

    // print each byte of k, starting with the first byte in memory
    for (int j = 0; j < 4; j++) {
        char byte = *address_of_k;
        printf("0x%x\n", byte & 0xff);
        address_of_k = address_of_k + 1;
    }

    return 0;
}
========

+ Exam prep
- In-class exam, Friday, October 6
- In Leighton 402 as usual
- Closed-everything-except-your-brain (no calculator, no notes)

- General topics
    - data representation
    - C

- 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 via classroom topics,
        homework assignments, sample programs, and the quiz

- What to study
    - homework assignments
    - quiz
    - sample code
    - class notes
    - backup reference material as needed: textbook readings

- Types of questions
    - Short answers
    - Here's some code; what's the output?
    - Write this tiny amount of code to do X (never more than 3-4 lines)
    - 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
    - byte order (little-endian vs. big-endian)

- Characters
    - difference between characters and C char
    - codepoints vs. encodings
    - ASCII (chart will be provided)
    - UTF-8 encoding (chart will be provided)
    - UTF-16 BE and UTF-16 LE

- [General C advice]
    - You can write your own experimental programs
        to see what happens when you do this or that

- 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, %p
    - [not on exam] fgets (including what if line is longer than buffer?)

- Null-terminated char strings
    - strlen
    - strcpy vs. strncpy (including what if source is longer than buffer in strncpy)
    - strcmp
    - printf %s vs. %p

- 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, also known as xor)

- C stuff that's pretty much the same as Java
    - if, else
    - &&, ||, !
    - while, for
    - {}, ()
    - +, -, / (int div), %
    - function signatures

+ Questions: bits, quiz, exam, whatever