CSC302 2007S, Class 11: Macros and More

Admin:
* Starting Friday, each person who arrives late will receive a
  penalty toward their final participation grade of 1 point
  per 5 minutes late or portion thereof.
* Don't forget Friday's lunch!
* Goal this week: Help you think better in C.
* Q on HW4?
* FOR FRIDAY:
  * How do I use comp in Quicksort?
  * How do I declare the comparator type?

Overview:
* Background: What is the C "perspective"?
* Background: Refactoring.
* A Domain: Quicksort.
* Macros: Basic Concepts.
* Enumerated Types.
* Macros: Some Hacks.

/Why use different languages?/
* Languages encourage us to think diffeently aboutt he programming task
* Different languages better meet different tasks
* Different langauges do have different efficiencies
  * Running code
  * Programmer time
* Once you've chosen a language, you should adopt the "worldview"
  of that language

/What is the C umwelt?/

* Expect to have direct control over memory
  * And to understand how computers use memory
  * Stacks and heaps, pointers are just integers, 
    data segment vs. code segment, virtual memory (maybe)
    * Detour: Virtual memory
* C programmers think about the underlying machine
* C programmers care about efficiency
* Low-level string processsing
  * A string is a 0-terminated array of characters
  * And arrays and pointers are indistinguishable

* Typical quick version of strcpy
  void strcpy(char *src, char *dest) 
  {
    while (*dest++ = *src++);
  }

  char html_request[128];
  strcpy(argv[1], html_request);

/General Good Programming Practice/

* Unit Testing
* Refactoring
  * Identify and "factor out" common code
  * Particularly good idea as alternative to cut-and-paste programming
* Sam: Good programmers can predict opportunities for refactoring,
  and write general code first
* XP/AP practice: Refactor only when you see or are about to write
  duplicated code
* Like functional programming, a technique for strong programmers

/An Example: Quicksort/

* How do we convert from "sort ints" to "sort floats"?
* How do we ease such conversions?
  * Typical strategy: Use "pointers to void" rather than int
  * Another strategy: Use typedef
  * Another strategy: Use #define
* Whoops!  I need to sort in increasing order, rather than decreasing