compiler knows that Friskycan’t bark because the Catclass doesn’t have a Bark()
method. The compiler wouldn’t even let Friskymeow if you didn’t define a Meow()
function.144 Day 6
DOuse the keyword classto declare a
class.
DOuse the dot operator (.) to access
class members and functions.DON’Tconfuse a declaration with a defi-
nition. A declaration says what a class is.
A definition sets aside memory for an
object.
DON’Tconfuse a class with an object.
DON’Tassign values to a class. Assign val-
ues to the data members of an object.DO DON’T
Private Versus Public Access ..............................................................................
Additional keywords are often used in the declaration of a class. Two of the most impor-
tant are publicand private.
The privateand publickeywords are used with members of a class—both data mem-
bers and member methods. Private members can be accessed only within methods of the
class itself. Public members can be accessed through any object of the class. This distinc-
tion is both important and confusing. All members of a class are private, by default.
To make this a bit clearer, consider an example from earlier:
class Cat
{
unsigned int itsAge;
unsigned int itsWeight;
void Meow();
};
In this declaration,itsAge,itsWeight, and Meow()are all private because all members
of a class are private by default. Unless you specify otherwise, they are private. If you
create a program and try to write the following within main(for example):
int main()
{
Cat Boots;
Boots.itsAge=5; // error! can’t access private data!
...
the compiler flags this as an error. In effect, by leaving these members as private,
you’ve said to the compiler, “I’ll access itsAge,itsWeight, and Meow()only from