CSC161 2010F, Class 04: An Introduction to C

Overview:
* About the C Programming Language.
* Some C Basics.
* Q & A.
* GNU/Linux Lab III, Continued.

Admin:
* Assignment 1 is due tonight.  Are there any questions?
  * How do I get rid of the psychologists?  It feels like grep should
    be helpful.  So read the man page.
* The next assignment should be available on Friday.
* Convo tomorrow.  Be there!
* For Friday, read Wikipedia on Emacs: http://en.wikipedia.org/wiki/Emacs.
* For Friday, read chapter 1 of Raymond.

What is C and why are we learning it?
* C is a programming language
  * Imperative programming language
    * Uh - Universally Helpful
    * Focuses on operations that change the state of the machine
      * Assignment (also I/O)
    * Primarily explicit rather than implicit sequencing of operations
  * Low-level
    * Reveals the underlying machine model
    * You get to take advantage of it
    * You have to understand it
* C is a moderately old language
  * Developed in early 1970's
  * First computers were ... 1940's
  * First high-level languages (not machine code or assembly) ... about 1960
  * Earlier languages: Fortran, LISP, Cobol, Algol
  * Newer languages: Java, Flash/Flex, ..., Ada, Scheme, Perl, 
* Small and coherent
  * ONE designer - Dennis Ritchie
  * Focus on building Unix
* Why C at Grinnell?
  * Learn underlying machine
  * You need some imperative language
  * C can be beautiful
  * Lots of languages derive from C
    * C++
    * C#
    * Java
    * JavaScript

In 151, you learned that there are six basic language features you need
to master in order to write programs that implement algorithms.

* Some set of basic operations and types
  * Assign to a variable
    VAR = EXP
  * Input
    getchar()
  * Ouput
    printf(...)
  * Increment a numeric variable
    ++var
    var++
  * Compare with <, ==, >, <=, >=, !=
* Variables- a way to name things
  * In C, these need explicit type
  * General form
    TYPE NAME;
  * Example
    int i;
* Repetition - a way to repeat basic operations
  while (TEST) 
    { 
      EXP;
    }
  for (INIT; TEST; INCREMENT)
    {
      EXP;
    }
* Conditionals - Make choices
  * Most common form
  if (TEST)
    CONSEQUENT
  else
    ALTERNATE
  * One-legged form
  if (TEST)
    CONSEQUENT
* A way to sequence operations
  * Separate with semicolons
  * Do one after another after another
* Functions/subroutines - encapsulate (and often name) some operations
  * Defining
    * Scheme
      (define func (lambda (params) body))
    * C
      RETURN_VALUE
      func(TYPED_PARAMS)
      {
        BODY
      }
    * E.g.,
      int
      silly(int x, int y)
      {
        x++;
        y--'
        return x+x*y;
      }
  * Calling
    * Scheme
      * (func arg1 arg2 ... argn)
    * C
      func(arg1, arg2, arg3)

Some Tips and More

* When using less, you can type /text to search for text, 'n' (no 
  quotation marks) searches for the next occurence