CTEC1335/2008F

Constants
---------

Variables that don't (and can't) vary.

Use the "const" keyword.

The compiler will prevent a constant's value from being modified (with
a compile error).


C/C++ Datatypes
===============

char 
unsigned char	8 bit integer / character / ASCII value

short
unsigned short	16 bit integer / word

int
unsigned	depends on CPU / operating system / compiler
		no smaller than short
		no larger than long

		on Intel 386, Windows XP, Visual C++ 2005, ints are 32 bits

long		
unsigned long	32 bit integer
		(64 bit integer on 64-bit CPU/ O/S / Compiler)

float		32 bit real number (IEEE format, 7 significant digits)

double		64 bit real number (IEEE format, 15 significant digits)

bool		Boolean:  true or false

char *		C-style string:
		array of characters with
		a null (zero) character at
		the end
		("zero terminated string")

string		C++ string


Declaring Constants
===================

These are for values that will not change during the program, or during
the programmer's lifetime.

You can also use constants to prevent "magic numbers" -- i.e., numeric
values that are hard-coded in your code.

Constants are useful for maintainability -- if you use a constant more
than once in your program, when you have to change it, you only need
to change it at a single line (the line where the constant is declared).

By definition, you must provide a value immediately -- because a constant's
value cannot be changed later!


const char SPACE = ' ' ;	// ASCII value for space

const int MAX_GRADE = 100 ;	// maximum grade for this course

const double PI = 3.14159265 ;	// pi


For strings, either a C-style string or C++ string is acceptable.  String
constants allow you to change your program's prompts, outputs or even
to translate your program into a language other than English.

const char * const GREETING = "Welcome to the machine!" ;

const string MESSAGE = "The program completed successfully" ;

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