CSC161 2010F, Class 31: Pointers

Overview:
* HW6
* More on Make
* More on HW5
* Pointer and Memory Basics
* Your Questions
* Lab

Admin:
* Cool Theatre stuff on campus this week.
* LoC Truck on Friday.
* Reading for tomorrow: K&R 5.3-5.4.
* Don't forget questions! 
* We'll go over some questions and issues on HW6.

HW 6

* What modifiers do you have for variables?  static and extern are two
  good ones.
* Is Google our friend for finding out about macros?
  * Yes.  As long as you spell correctly.
* What should a Boolean function, such as is_prime, return?
  * An integer
  * 1 for "true" (or any positive number)
  * 0 for "false"
* How do we build the Fibonacci sequence non-recursively
  F_prev = 0
  F_current = 1
  repeat lots of times
    F_next = F_prev + F_current
    F_prev = F_current
    F_current = F_next
* Is there a remainder function?
  * Mod (%) should suffice

HW 5

* Systematic checks of sorting involves building lots of permutations

Make

* Skipped for time issues

Pointers

* Operator: & (address-of) gives the address (location in memory) of
  a variable.
  ip = &x;
* You need to be able to do interesting things with addresses.
  * Find out what value is stored at that address
    printf ("%d", *ip);
  * Change what is stored at that address
    *ip = ...
* Variables of poitner type
  type *variable;
  int *ip;

Your Questions

* Couldn't you also return the new a and b instead of making swap a void functio
  NO.  C only lets you return/assign one value at a time
n?
* In the swap routine example, are pointers the only way to make that function work?
  YES, if you restrict yourself to writing a function
  BUT a macro could work: #define SWAP(X,Y) { temp = X; X = Y; Y = temp; }
    swap (a[i++], b[j++]);
* Could you explain the * operator?  It seems clearly laid out on page 94, but I'm just not wrapping my head all the way around it.

Other Questions

* !! - the last command
* !number - command number N (determine by history)
* !text - the last command that began with text
* !$ - the last item on the previous line

mkdir /home/rebelsky/foo
cd !$

* ^text^replacement
  Redoes the last command, replacing the FIRST INSTANCE of text with replacement