Lecture
The purpose of introducing the concept of classes in C ++ is to provide the programmer with the means to create new types that are as easy to use as the built-in types. The type is a concrete representation of some concept. For example, the built-in type C ++ float along with the operations +, -, *, etc. is the embodiment of the mathematical concept of a real number. A class is a user-defined type. We create a new type to define a concept that is not expressed directly by built-in types. For example, we could enter the type of TrunkLine (long-distance line) in the program related to telephony, the type Depositir (depositor) in the program of bank management or the type Pretator (predator) in the program of environmental modeling.
A class is a fundamental concept of C ++ and underlies many properties of C ++. The class provides a mechanism for creating objects. The class reflects the most important concepts of object-oriented programming: encapsulation, inheritance, polymorphism.
In terms of syntax, a class in C ++ is a structured type formed on the basis of already existing types.
In this sense, the class is an extension of the concept of structure. In the simplest case, a class can be defined using the following construction:
class_type class_name {class_list_list};
Where
class_type is one of the service words class, struct, union ;
class_name is an identifier;
class_ member_list - definitions and descriptions of typed data and class-related functions.
Functions are class methods that define operations on an object.
Data is the fields of an object that make up its structure. The field values determine the state of the object.
We will call class members as class components, distinguishing component data and component functions.
Example 1.1.1
struct date // date
{int month, day, year; // fields: month, day, year
void set (int, int, int); // method - set the date
void get (int *, int *, int *); // method - get date
void next (); // method - set the next date
void pri nt (); // method - display the date
};
Example 1.1.2
Example 1.1.2
struct complex // complex number
{double re, im;
double real () {return (re);}
double imag () {return (im);}
void set (double x, double y) {re = x; im = y;}
void print () {cout << ”re =” << re; cout << “im =” << im;}
};
To describe an object of a class (class instance), the construction is used
class_name object_name
date today, my_birthday;
date * point = & today; // pointer to date object
date clim [30]; // array of objects
date & name = my_birthday; // object reference
The objects defined include data that corresponds to the data members of the class. Member functions of a class allow processing data of specific objects of a class. You can access the data of an object and call functions for an object in two ways. First, with the help of “qualified” names:
object_name.class_name:: data_name
object_name.class_name:: function_name
Class name may be omitted
object_name.data_name
object_name.function_name
For example:
class “complex number”
complex x1, x2;
x1.re = 1.24;
x1.im = 2.3;
x2.set (5.1,1.7);
x1.print ();
The second access method uses a pointer to an object.
pointer_to_object–> component_name
complex * point = & x1; // or point = new complex;
point -> re = 1.24;
point -> im = 2.3;
point -> print ();
Example 1.1.3
// Class “goods”
intpercent = 12; // markup
struct goods
{char name [40];
float price;
void Input ()
{cout << “name:”;
cin >> name;
cout << “price:”;
cin >> price;}
void print ()
{cout << “\ n” << name;
cout << “, price:”;
cout << long (price * (1.0 + percent * 0.01));}
};
void main (void)
{goods wares [5];
int k = 5;
for (int i = 0; i
cout << “\ nList of goods at mark-up” << percent << “%”;
for (i = 0; i
percent = 10;
cout << “\ nList of goods at mark-up” << percent << "%";
goods * pGoods = wares;
for (i = 0; i print ();
}
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