Notes for Lecture 6 - February 1, 2007
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* Type double revisited

** Representation
*** 3 fields
**** sign bit
**** exponent (11 bits)
**** significant (53 bits, including hidden leading 1 bit)
*** See http://en.wikipedia.org/wiki/IEEE_754 for further information

** float.h contains several constants describing range and limits of doubles
See demo 06.1_dbl for further information

** Doubles can be converted to ints.
*** Meaning:  drop fractional part (i.e., truncate towards zero)
*** Examples:  -2.71 ==> -2,  3.4 ==> 3.
*** Explicit cast:  (int)e, where e is an expression of type double
*** Implicit via assignment:  k=e; where k is int and e is double. 
*** Implicit from function: return e; where e is double and function returns int.
See demo 06.1_dbl.

* 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 06.2_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>.)
** 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
See demo 06.3_files

* Returning multiple values from a function
** Can return results through pointer arguments (like scanf() does)
** Example:  to return two doubles val1 and val2:
*** Function prototype:  myfun( double* xp, double* yp );
*** Function call:  myfun( &x, &y ), where x and y are variables of type double
*** Within definition of myfun(): *xp = val1; *yp = val2.
** Actual meaning of & and * will be described later.
See demo 06.4_ptrargs