What’s a structure? W hat’s the keyword to define a structure?
What are structures u sed for?
Is a structure definitio n an executable statement? Can i t be put
in a header file?
Why includein g a header file with a structur es definition
multiple times is a pro blem? How is this problem solved ?
What are #defi ne #ifndef #endif?
What is a structure va riable?
How are elements of a structure called?
Do elements of the sa me structure (different structures) have to
have unique names?
How can structures b e initialized? What happens when one
structure variable is a ssigned the value of another?
Can structures be pas sed as parameters? by value? by
reference? Can a fun ction return a structure?
Structures Revisited
Classes
Structure is an aggregate construct providing encapsulation
encapsulation - combining a number of items in a single entity
consider implementing date:
as structure:
struct Date{
int month;
int day;
int year;
};
and a set of functions manipulating dates:
void set_date(Da te &d, int, i nt, int);
void add_year(Date &d, int n);
bool compare(Date &d1, Date &d2);
problems:
there is no explicit connection between data type (structure) and these
functions
it does not specify that the functions listed should be the only ones that
access and modify date variables
– if there is a bug in Date manipulation - it can be anywhere in the program
– if modification of Date is needed - all program needs to be updated
What’s Wrong with Structures?
Class is an aggregate data type
Class may contain member variables and member functions
member variables and member function prototypes are declared within class
definition
member functions can manipulate member variables without accepting them as
parameters
class Date { // class name
public: // ignore this for now
void set(int, int, int) ;
int getda y();
int month;
int day;
int year;
}; // don’t forget the semic olon
a variable of type class is called object (how is a variable of type structure
called?)
Date mybday;
each object has member variables and can call member functions of its class.
Addressing the members is done using dot-operator:
mybday.set(10, 26, 68);
cout << mybd ay.day;
Class Definition
public/private attributes control the way the class members are accessed (why
do we want to do that?)
public member can be accessed within member functions and directly (with dot
operator)
private member - can only be accessed within member functions
class Date { // class name
public:
void set(int, int, int) ;
int getda y();
private:
int month;
int day;
int year;
}; // don’t forget semicolon
make member variables private, make functions either public or private. This
restricts manipulation of variables to member function which makes debugging
and changes in class easier
examples:
mybday.set(10, 5, 99); // good
mybday.year=99; // ERROR - private member
Public and Private Members
functions can be defin ed either inside or outside class d efinition
outside definition - cla ss name (called type qualifier) and scope
resolution operator (::) precedes function name:
void Date::set(i nt m, int d, int y){
month=m; // no dot with member variables
day=d; // no declaration of member variables
year=y;
}
to define inside - repla ce prototype with definition
class Date {
public:
void set(int, int, int) ;
int getda y(){return(day); }; //still need s “;”
private:
int month;
int day;
int year;
}; // don’t forget semicolon
function defined insid e is called in-line function - at com pilation the
function code replace s every invocation - use only for s mall functions
Member Function Definitions
