Every object of a given class incorporates the same combination of things, specifically, the set of data values as member
variables of the class that characterize an object and the set of operations as member functions of the class.
This packaging of data values and functions within an object is referred to as encapsulation.
The ability to make the data values for an object generally inaccessible is called data hiding or information hiding.
A class is a user - defined data type.
• The variables and functions defined within a class are members of the class.The variables are member variables, and the functions are member functions.
Member functions are also often referred to as methods; member variables are called either data members or fields.
• Variables of a class type store objects. Objects are sometimes called instances of the class.Defining an instance of a class is referred to as instantiation.
public and private precede a sequence of members that are or are not accessible outside the class. The specification of public or private applies to all members that follow until there is a different specification. You could omit the first private specification here and get the default status of private, but it’s better to make it explicit. Members in a private section of a class can be accessed only from functions that are members of the same class. Member variables or functions that need to be accessed by a function that is not a member of the class must be specified as public. A member function can reference any other member of the same class, regardless of the access specification, by just using its name.
#include "pch.h"
#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
// Function to calculate the volume of a box
double volume()
{
return length * width * height;
}
};
int main()
{
Box myBox; // A Box object with all dimensions 1
std::cout << "Volume of myBox is " << myBox.volume() << std::endl; // Volume is 1.0
}#include <iostream>
class Box
{
public:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
// Function to calculate the volume of a box
double volume()
{
return length * width * height;
}
};
int main()
{
Box myBox; // A Box object with all dimensions 1
myBox.length = 1.5;
myBox.width = 2.0;
myBox.height = 4.0;
std::cout << "Volume of myBox is " << myBox.volume() << std::endl; // Volume is 12.0
}Structures and classes are nearly completely equivalent.You define a structure in the same way as a class, only using the struct keyword instead of the class keyword.The main difference between the two is that in contrast to members of a class, the members of a structure are public by default.
#include <iostream>
/*A class constructor is a special kind of function in a class that differs in a few significant respects from
an ordinary member function. A constructor is called whenever a new instance of the class is defined. It
provides the opportunity to initialize the new object as it is created and to ensure that member variables
contain valid values. A class constructor always has the same name as the class.
A constructor does not return a value and therefore has no return type.
If you don’t define a constructor for a class, the compiler will supply a default default
constructor.
A default constructor is a constructor that can be called without arguments. If you do not define any
constructor for a class—so no default constructor or any other constructor—the compiler generates a default
constructor for you. That’s why it’s called a default default constructor; it is a default constructor that is
generated by default. A compiler-generated default constructor has no parameters, and its sole purpose is
to allow an object to be created.
as soon as you do define any constructor, even a nondefault one with parameters, the default default
constructor is no longer supplied. There are circumstances in which you need a constructor with no parameters
in addition to a constructor that you define that has parameters. In this case, you must ensure that there is
a definition for the no-arg constructor in the class.
*/
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
// The default constructor that was supplied by the compiler...
Box()
{
// Empty body so it does nothing...
}
public:
// Function to calculate the volume of a box
double volume()
{
return length * width * height;
}
};
int main()
{
Box myBox; // A Box object with all dimensions 1
std::cout << "Volume of myBox is " << myBox.volume() << std::endl; // Volume is 1
}
// Defining a class constructor
#include <iostream>
// Class to represent a box
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
// Constructor
Box(double lengthValue, double widthValue, double heightValue)
{
std::cout << "Box constructor called." << std::endl;
length = lengthValue;
width = widthValue;
height = heightValue;
}
// Function to calculate the volume of a box
double volume()
{
return length * width*height;
}
};
int main()
{
Box firstBox{ 80.0, 50.0, 40.0 }; // Create a box
double firstBoxVolume{ firstBox.volume() }; // Calculate the box volume
std::cout << "Volume of Box object is " << firstBoxVolume << std::endl;
/*once you define a constructor, the compiler won’t supply a default constructor
anymore, at least not by default. That means the following statement will no longer compile.*/
// Box secondBox; // Causes a compiler error message
}// Defining a class constructor
#include <iostream>
// Class to represent a box
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
// Constructor
Box(double lengthValue, double widthValue, double heightValue)
{
std::cout << "Box constructor called." << std::endl;
length = lengthValue;
width = widthValue;
height = heightValue;
}
//Box() {} // the first way of defining a default constructor
Box() = default; //the second way of defining a default constructor; the preferred way.
// Function to calculate the volume of a box
double volume()
{
return length * width*height;
}
};
int main()
{
Box secondBox; // Create a box
double secondBoxVolume{ secondBox.volume() }; // Calculate the box volume
std::cout << "Volume of Box object is " << secondBoxVolume << std::endl;
}// Defining functions and constructors outside the class definition
#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
// Constructors
Box(double lengthValue, double widthValue, double heightValue);
Box() = default;
// Function to calculate the volume of a box
double volume();
};
// Constructor definition
Box::Box(double lengthValue, double widthValue, double heightValue)
{
std::cout << "Box constructor called." << std::endl;
length = lengthValue;
width = widthValue;
height = heightValue;
}
// Function to calculate the volume of a box
double Box::volume()
{
return length * width*height;
}
int main()
{
Box firstBox{ 80.0, 50.0, 40.0 }; // Create a box
double firstBoxVolume{ firstBox.volume() }; // Calculate the box volume
std::cout << "Volume of the first Box object is " << firstBoxVolume << std::endl;
Box secondBox; // Uses compiler-generated default constructor
double secondBoxVolume{ secondBox.volume() }; // Calculate the box volume
std::cout << "Volume of the second Box object is " << secondBoxVolume << std::endl;
}// Default Constructor Parameter Values
#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
// A constructor for which all parameters have a default value counts as a default constructor.
Box(double lv = 2.0, double wv = 2.0, double hv = 2.0);
// Function to calculate the volume of a box
double volume();
};
// Constructor definition
Box::Box(double lengthValue, double widthValue, double heightValue)
{
std::cout << "Box constructor called." << std::endl;
length = lengthValue;
width = widthValue;
height = heightValue;
}
// Function to calculate the volume of a box
double Box::volume()
{
return length * width*height;
}
int main()
{
Box firstBox;
double firstBoxVolume{ firstBox.volume() };
std::cout << "Volume of the first Box object is " << firstBoxVolume << std::endl;//output 8
Box secondBox{ 80.0, 50.0, 40.0 };
double secondBoxVolume{ secondBox.volume() };
std::cout << "Volume of the first Box object is " << secondBoxVolume << std::endl;//output 160000
}#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
// A constructor for which all parameters have a default value counts as a default constructor.
Box(double lv = 2.0, double wv = 2.0, double hv = 2.0);
// Function to calculate the volume of a box
double volume();
};
// Constructor definition using a member initializer list
Box::Box(double lv, double wv, double hv) : length{ lv }, width{ wv }, height{ hv }
{
std::cout << "Box constructor called." << std::endl;
}
// Function to calculate the volume of a box
double Box::volume()
{
return length * width*height;
}
int main()
{
Box firstBox;
double firstBoxVolume{ firstBox.volume() };
std::cout << "Volume of the first Box object is " << firstBoxVolume << std::endl;//output 1
Box secondBox{ 80.0, 50.0, 40.0 };
double secondBoxVolume{ secondBox.volume() };
std::cout << "Volume of the first Box object is " << secondBoxVolume << std::endl;//output 160000
}// Using a delegating constructor
#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
// Constructors
Box(double lv, double wv, double hv);
explicit Box(double side); // Constructor for a cube
Box() = default; // No-arg constructor
double volume(); // Function to calculate the volume of a box
};
// Constructor definition
Box::Box(double lv, double wv, double hv)
: length{ lv }, width{ wv }, height{ hv }
{
std::cout << "Box constructor 1 called." << std::endl;
}
// Constructor for Box that is a cube
Box::Box(double side) : Box{ side, side, side }
{
std::cout << "Box constructor 2 called." << std::endl;
}
// Function to calculate the volume of a box
double Box::volume()
{
return length * width*height;
}
int main()
{
Box box1{ 2.0, 3.0, 4.0 }; // An arbitrary box
/*Creating the second object calls constructor 1 followed by constructor 2.*/
Box box2{ 5.0 }; // A box that is a cube
std::cout << "box1 volume = " << box1.volume() << std::endl;
std::cout << "box2 volume = " << box2.volume() << std::endl;
/* compiler supplied a default copy constructor, which is a constructor that creates an object by copying an existing object. The
default copy constructor copies the values of the member variables of the object that is the argument to the
new object.*/
Box box3{ box2 };
std::cout << "box3 volume = " << box3.volume() << std::endl; // Volume = 125
}#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
// Constructors
Box(double lv, double wv, double hv);
explicit Box(double side); // Constructor for a cube
Box() = default; // No-arg constructor
Box(const Box& box);//the Copy Constructor
double volume(); // Function to calculate the volume of a box
};
// Constructor definition
Box::Box(double lv, double wv, double hv)
: length{ lv }, width{ wv }, height{ hv }
{
std::cout << "Box constructor 1 called." << std::endl;
}
// Constructor for Box that is a cube
Box::Box(double side) : Box{ side, side, side }
{
std::cout << "Box constructor 2 called." << std::endl;
}
//copy constructor
Box::Box(const Box& box) : length{ box.length }, width{ box.width }, height{ box.height }
{
std::cout << "Box constructor 3 called." << std::endl;
}
// Function to calculate the volume of a box
double Box::volume()
{
return length * width*height;
}
int main()
{
Box box1{ 2.0, 3.0, 4.0 }; // An arbitrary box
/*Creating the second object calls constructor 1 followed by constructor 2.*/
Box box2{ 5.0 }; // A box that is a cube
std::cout << "box1 volume = " << box1.volume() << std::endl;
std::cout << "box2 volume = " << box2.volume() << std::endl;
Box box3{ box2 };
std::cout << "box3 volume = " << box3.volume() << std::endl; // Volume = 125
}#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
Box(double lv, double wv, double hv);
Box() = default;
double volume();
double getLength() { return length; }
double getWidth() { return width; }
double getHeight() { return height; }
Box* setLength(double lv) {
if (lv > 0) length = lv;
return this;
}
Box* setWidth(double wv) {
if (wv > 0) width = wv;
return this;
}
Box* setHeight(double hv) {
if (hv > 0) height = hv; return this;
}
};
// Constructor definition
Box::Box(double lv, double wv, double hv)
: length{ lv }, width{ wv }, height{ hv }
{
std::cout << "Box constructor 1 called." << std::endl;
}
double Box::volume()
{
return this->length * this->width*this->height;
}
int main()
{
Box myBox{ 3.0, 4.0, 5.0 };
std::cout << "myBox dimensions are " << myBox.getLength()
<< " by " << myBox.getWidth()
<< " by " << myBox.getHeight() << std::endl;
myBox.setLength(-20.0)->setWidth(40.0)->setHeight(10.0); // Set all dimensions of myBox
/*Because the mutator functions return the this pointer, you can use the value returned by one function
to call the next. */
std::cout << "myBox dimensions are now " << myBox.getLength() // 3 (unchanged)
<< " by " << myBox.getWidth() // by 40
<< " by " << myBox.getHeight() << std::endl; // by 10
}
#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
Box(double lv, double wv, double hv);
Box() = default;
double volume();
double getLength() { return length; }
double getWidth() { return width; }
double getHeight() { return height; }
Box& setLength(double lv) {
if (lv > 0) length = lv;
/*returning references to *this*/
return *this;
}
Box& setWidth(double wv) {
if (wv > 0) width = wv;
return *this;
}
Box& setHeight(double hv) {
if (hv > 0) height = hv;
return *this;
}
};
Box::Box(double lv, double wv, double hv)
: length{ lv }, width{ wv }, height{ hv }
{
std::cout << "Box constructor 1 called." << std::endl;
}
double Box::volume()
{
return length * width * height;
}
int main()
{
Box myBox{ 3.0, 4.0, 5.0 };
std::cout << "myBox dimensions are " << myBox.getLength()
<< " by " << myBox.getWidth()
<< " by " << myBox.getHeight() << std::endl;
/*The following pattern is called method chaining. */
myBox.setLength(-20.0).setWidth(40.0).setHeight(10.0); // Set all dimensions of myBox
std::cout << "myBox dimensions are now " << myBox.getLength() // 3 (unchanged)
<< " by " << myBox.getWidth() // by 40
<< " by " << myBox.getHeight() << std::endl; // by 10
}#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
public:
Box(double lv, double wv, double hv);
Box() = default;
double getLength() const { return length; }
double getWidth() const { return width; }
double getHeight() const { return height; }
};
Box::Box(double lv, double wv, double hv)
: length{ lv }, width{ wv }, height{ hv }
{
std::cout << "Box constructor 1 called." << std::endl;
}
int main()
{
const Box myBox{ 3.0, 4.0, 5.0 };
std::cout << "myBox dimensions are " << myBox.getLength()
<< " by " << myBox.getWidth()
<< " by " << myBox.getHeight() << std::endl;
/*For const objects you can only call const member functions. */
}
#include <iostream>
int main()
{
double length{ 10 };
double& length1 = length;
double length2 = length;
length1 = 20;
std::cout << length << std::endl;//output 20
length2 = 30;
std::cout << length << std::endl;//output 20
}// Defining mutable member variables that can be modified within const member functions
#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
mutable unsigned count{};
public:
// Constructors
Box() = default;
Box(double length, double width, double height);
double volume() const; // Function to calculate the volume of a box
void printVolume() const; // Function to print out the volume of a box
// Functions to provide access to the values of member variables
double getLength() const { return length; }
double getWidth() const { return width; }
double getHeight() const { return height; }
// Functions to set member variable values
void setLength(double lv) { if (lv > 0) length = lv; }
void setWidth(double wv) { if (wv > 0) width = wv; }
void setHeight(double hv) { if (hv > 0) height = hv; }
};
// Constructor definition
Box::Box(double lv, double wv, double hv)
: length{ lv }, width{ wv }, height{ hv }
{
}
// Function to calculate the volume of a box
double Box::volume() const
{
return length * width * height;
}
// Function to print the volume of a Box to std::cout
void Box::printVolume() const
{
// Count how many times printVolume() is called using a mutable member in a const function
std::cout << "The volume of this box is " << volume() << std::endl;
std::cout << "printVolume() has been called " << ++count << " time(s)" << std::endl;
}
int main()
{
Box myBox{ 3.0, 4.0, 5.0 };
myBox.printVolume();
myBox.setHeight(55.5);
myBox.printVolume();
// Even for constant Boxes mutable member variables can be modified:
const Box constBox{ 1.0, 2.0, 3.0 };
constBox.printVolume();
constBox.printVolume();
}
// Using a friend function of a class
#include <iostream>
#include <memory>
class Box
{
private:
double length;
double width;
double height;
public:
// Constructors
Box(double lv = 1.0, double wv = 1.0, double hv = 1.0);
double volume() const; // Function to calculate the volume of a box
friend double surfaceArea(const Box& aBox); // Friend function for the surface area
};
// Constructor definition
Box::Box(double lv, double wv, double hv) : length{ lv }, width{ wv }, height{ hv }
{
std::cout << "Box constructor called." << std::endl;
}
// Function to calculate the volume of a box
double Box::volume() const
{
return length * width*height;
}
int main()
{
Box box1{ 2.2, 1.1, 0.5 }; // An arbitrary box
Box box2; // A default box
/*create a smart pointer to a Box object allocated in the free store*/
auto box3 = std::make_unique<Box>(15.0, 20.0, 8.0); // Dynamically allocated Box
std::cout << "Volume of box1 = " << box1.volume() << std::endl;
std::cout << "Surface area of box1 = " << surfaceArea(box1) << std::endl;
std::cout << "Volume of box2 = " << box2.volume() << std::endl;
std::cout << "Surface area of box2 = " << surfaceArea(box2) << std::endl;
std::cout << "Volume of box3 = " << box3->volume() << std::endl;
std::cout << "Surface area of box3 = " << surfaceArea(*box3) << std::endl;
}
// friend function to calculate the surface area of a Box object
double surfaceArea(const Box& aBox)
{
return 2.0 * (aBox.length * aBox.width + aBox.length * aBox.height + aBox.height * aBox.width);
}
#include <iostream>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
/*Static member variables of a class are associated with the class as a whole, not with any particular object of
the class. When you declare a member variable of a class as static, the static member variable is defined
only once and will exist even if no class objects have been created. Each static member variable is accessible
in any object of the class and is shared among however many objects there are. An object gets its own
independent copies of the ordinary member variables, but only one instance of each static member variable
exists, regardless of how many class objects have been defined.*/
static inline size_t objectCount{}; // Count of objects in existence
public:
/* Constructors */
Box(double lv, double wv, double hv);
Box(double side); // Constructor for a cube
Box(); // Default constructor
Box(const Box& box); // Copy constructor
double volume() const; // Function to calculate the volume of a box
size_t getObjectCount() const { return objectCount; }
};
Box::Box(double lv, double wv, double hv) // Constructor definition
: length{ lv }, width{ wv }, height{ hv }
{
++objectCount;
std::cout << "Box constructor 1 called." << std::endl;
}
Box::Box(double side) : Box{ side, side, side } // Constructor for a cube
{
std::cout << "Box constructor 2 called." << std::endl;
}
Box::Box() // Default constructor
{
++objectCount;
std::cout << "Default Box constructor called." << std::endl;
}
Box::Box(const Box& box) // Copy constructor
: length{ box.length }, width{ box.width }, height{ box.height }
{
++objectCount;
std::cout << "Box copy constructor called." << std::endl;
}
// Function to calculate the volume of a box
double Box::volume() const
{
return length * width * height;
}
int main()
{
const Box box1{ 2.0, 3.0, 4.0 }; // An arbitrary box
Box box2{ 5.0 }; // A box that is a cube
std::cout << "box1 volume = " << box1.volume() << std::endl;
std::cout << "box2 volume = " << box2.volume() << std::endl;
Box box3{ box2 };
std::cout << "box3 volume = " << box3.volume() << std::endl; // Volume = 125
std::cout << std::endl;
/*The initial values for the first three array elements are existing objects, so the compiler calls the copy
constructor to duplicate box1, box2, and box3. The fourth element is initialized with an object that
is created in the braced initializer for the array by the constructor 2, which calls constructor 1 in its
initialization list. The last two array elements have no initial values specified, so the compiler calls the
default constructor to create them.*/
Box boxes[6]{ box1, box2, box3, Box {2.0} };
std::cout << sizeof boxes << std::endl;//ouput 144
std::cout << sizeof Box << std::endl;//output 24
/*only one copy of the static member objectCount exists, and all the
constructors are updating it. The getObjectCount() function is called for the box1 object, but you could use
any object including any of the array elements to get the same result. */
std::cout << "\nThere are now " << box3.getObjectCount() << " Box objects." << std::endl;//output 9
}
// Defining and accessing static constants
#include <iostream>
#include <string>
#include <string_view>
class CylindricalBox
{
public:
static inline const float maxRadius{ 35.0f };
static inline const float maxHeight{ 60.0f };
static inline const std::string defaultMaterial{ "paperboard" };
CylindricalBox(float radius, float height, std::string_view material = defaultMaterial);
double volume() const;
private:
// The value of PI used by CylindricalBox's volume() function
static inline const float PI{ 3.141592f };
double radius;
double height;
std::string material;
};
CylindricalBox::CylindricalBox(float r, float h, std::string_view mat)
: radius(r)
, height(h)
, material(mat)
{
}
double CylindricalBox::volume() const
{
return PI * radius * radius * height;
}
int main()
{
const CylindricalBox bigBox{ 1.23f, CylindricalBox::maxHeight, CylindricalBox::defaultMaterial };
std::cout << "The volume of bigBox is " << bigBox.volume() << std::endl;
}// Implementing a destructor
#include <iostream>
#include <memory>
class Box
{
private:
double length{ 1.0 };
double width{ 1.0 };
double height{ 1.0 };
static inline size_t objectCount{}; // Count of objects in existence
public:
// Constructors
Box(double lv, double wv, double hv);
Box(double side); // Constructor for a cube
Box(); // Default constructor
Box(const Box& box); // Copy constructor
double volume() const; // Function to calculate the volume of a box
static size_t getObjectCount() { return objectCount; }
~Box(); // Destructor
};
// Constructor definition
Box::Box(double lv, double wv, double hv) : length{ lv }, width{ wv }, height{ hv }
{
++objectCount;
std::cout << "Box constructor 1 called." << std::endl;
}
Box::Box(double side) : Box{ side, side, side } // Constructor for a cube
{
std::cout << "Box constructor 2 called." << std::endl;
}
Box::Box() // Default constructor
{
++objectCount;
std::cout << "Default Box constructor called." << std::endl;
}
Box::Box(const Box& box) // Copy constructor
: length{ box.length }, width{ box.width }, height{ box.height }
{
++objectCount;
std::cout << "Box copy constructor called." << std::endl;
}
Box::~Box() // Destructor
{
std::cout << "Box destructor called." << std::endl;
--objectCount;
}
// Function to calculate the volume of a box
double Box::volume() const
{
return length * width*height;
}
int main()
{
std::cout << "There are now " << Box::getObjectCount() << " Box objects." << std::endl;
const Box box1{ 2.0, 3.0, 4.0 }; // An arbitrary box
Box box2{ 5.0 }; // A box that is a cube
std::cout << "There are now " << Box::getObjectCount() << " Box objects." << std::endl;
for (double d{}; d < 3.0; ++d)
{
Box box{ d, d + 1.0, d + 2.0 };
std::cout << "Box volume is " << box.volume() << std::endl;
}
std::cout << "There are now " << Box::getObjectCount() << " Box objects." << std::endl;
auto pBox = std::make_unique<Box>(1.5, 2.5, 3.5);
std::cout << "Box volume is " << pBox->volume() << std::endl;
std::cout << "There are now " << pBox->getObjectCount() << " Box objects." << std::endl;
}Members of a class can be specified as public, in which case they are freely accessible from any function in a program.Alternatively, they can be specified as private, in which case they may be accessed only by member functions, friend functions of the class, or members of nested classes.
#include <cstdlib> // For random number generation
#include <ctime> // For the std::time() function
#include <iostream>
// Function to generate a random integer 1 to 100
inline double random()
{
return 1.0 + rand() / (RAND_MAX / 100 + 1);
}
int main()
{
std::srand((unsigned)std::time(0)); // Initialize the random number generator
int count{};
std::cout << "Do you want to generate a number from 1 to 100? Answer Y to continue" << std::endl;
char answer{};
std::cin >> answer;
while (answer == 'Y')
{
std::cout << random() << std::endl;
std::cout << "Do you want to generate a number from 1 to 100? Answer Y to continue" << std::endl;
std::cin >> answer;
}
}