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Notes for Lecture 8 - February 7, 2008
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* Arrays and subscripts

** Array storage block of type T
Consists of a consecutive sequence of data objects (unnamed variables)
of type T.  If the first object is at address a, then subsequent
objects in the sequence are at addresses a+k, a+2k, a+3k, ..., where k
= sizeof(T).
See demo demos-08/1-scan.

** Accessing object in an array
*** References to objects of an array
If e is a reference of type T to the first data object in an array
storage block, then e, e+1, e+2, e+3 are references to the successive
data objects in the block.
*** Subscript notation
**** Syntax:  e[k]
Here e is a reference-valued expression of type T and k an integer.
**** Semantics: Same as *(e+k)
Thus, e[k] is the variable of type T at position k in the array
storage block, where variables are numbered beginning with 0.  
Can use e[k] just like any other variable of type T.
Example: e[k] = e[k-1] + 3;
Example: &e[k] is a reference to e[k].  It is the same as (e+k).
**** Usage
Subscript notation is clearer and more natural for referencing the
data objects in an array storage block.
Use it in preference to *(e+k).
See demo demos-08/2-ptrargs and demos-08/4-smooth.

* Command line arguments
** String arguments passed by shell from command line to the program
** Example:  mycommand foo 123   has two string arguments: "foo" and "123".
** Main program must have the prototype:
int main( int argc, char* argv[] )
*** argc:  number of strings in argv[]
*** argv:  strings passed in argv[0]...argv[argc-1].
*** argv[0]: leaf name or full path name used to invoke the command
*** argv[1]: first argument following command name
*** argv[2]: second argument following command name, etc.
** Example:
mycommand foo 123  would result in argc==3 and argv[0]...argv[2] containing
three strings:  "mycommand", "foo", and "123".
See demo demos-08/3-cmdline.

* Files and streams
** Definitions:
A file is a sequence of bytes stored on disk.
An input stream is a source of bytes from a file, keyboard, or other device
An output stream is a sink of bytes, going to a file, screen, or other device
** Three streams are open by default:
*** stdin (standard input)
*** stdout (standard output)
*** stderr (standard error) [we haven't discussed this yet]
** fopen()
*** creates a new stream from/to a file
*** Return type of fopen() is FILE*.  (FILE is defined in <stdio.h>.)
*** Use errno and perror() or strerror to identify and/or report error.
** Open for reading: fopen( filename, "r" )
*** filename is string giving name of a file
*** "r" specifies to open the file for reading
*** fopen returns NULL if it fails to open the file
*** fopen creates a new input stream if successful and returns a pointer to it.
** reading from a stream
*** getchar() and scanf() read from stdin
*** getc(), fgetc(), and fscanf() take an extra stream argument and read from it
*** ungetc() allows one character to be put back into stream
*** scanf() can be used to skip fields of input using "*" modifier
Example:  scanf( "%*s" ); skips forward to first whitespace following
          non-whitespace
See demo demos-08/5-files