Experiment 4 operator overloading and virtual functions

• Experimental purpose or task

Object oriented software development method is a software development method developed by absorbing useful concepts and effective methods in the field of software engineering . It sets abstraction 、 encapsulation 、 Inheritance and polymorphism in one , It can help programmers develop modularity 、 High degree of data abstraction , Reflect information concealment 、 Reusable 、 Easy to modify 、 Easy to transplant and other features of the program . 

This course is based on C++ The object-oriented mechanism in the language is mainly , Discuss the basic idea and method mechanism of object-oriented programming . Through the experimental teaching link , Enable learners to pass a certain amount of program examples and related exercises in the learning process , Gradually master C++ Process oriented and object-oriented functions , So as to master the basic knowledge and skills of object-oriented programming .

Through this experimental teaching link , It can improve learners' professional ability in the following aspects ：

1. Improve learners' abstract ability and logical thinking ability to solve problems ;
2. Preliminarily master the object-oriented software design ideas ;
3. Improve learners' self-learning ability of object-oriented program development tools ;
4. Make learners have the basic literacy of object-oriented program development .

• Basic requirements of experimental teaching

1. Understand and master C++ Advanced features of language functions , Understand the data abstraction and data encapsulation of object-oriented programming , master C++ The mechanism and method of data encapsulation and information hiding through classes and objects ;
2. Understand the design idea of object-oriented programming code reuse , master C++ Class inheritance and derivation mechanism and implementation approach ;
3. Understand the concept and idea of polymorphism in object-oriented programming , master C++ Operation overload 、 function overloading 、 The mechanism and method of realizing polymorphism by virtual function Technology ;
4. Understand and master C++ I/O The idea and method of device independence of stream to realize input and output .

Summary

1. For classes MyString, Overload required ‘+’ Operator can be used to evaluate the expression :a=b+c; Represents the connection of two strings . among a,b,c Is the class MyString The object of .

2. Use virtual function programming to calculate the volume and surface area of sphere and cylinder . Because both sphere and cylinder can be regarded as inherited from circle , So you can define the circle class Circle As the base class . stay Circle Class to define a data member radius And two virtual functions area() and volume(). from Circle Class derivation Sphere Classes and Column class . For virtual functions in derived classes area() and volume() Redefinition , Calculate the volume and surface area of sphere and cylinder respectively .

The basic requirements

Overload the corresponding operators and write programs , Be able to use virtual functions to write programs, test and submit programs .

#include<iostream>
#include<cstring>
using namespace std;


class Mystring {
public:
	Mystring(const char* ptr = "")
		:_ptr(new char[strlen(ptr) + 1])
	{
		strcpy(_ptr, ptr);
	}

	Mystring operator+(Mystring& s) {
		int len1 = strlen(_ptr);
		int len2 = strlen(s._ptr);

		char* tmp = new char[len1 + len2 + 1];

		strcpy(tmp, _ptr);
		strcpy(tmp + len1, s._ptr);
		
		Mystring ret(tmp);

		delete[] tmp;
		return ret;
	}
	friend ostream& operator<<(ostream& _cout, Mystring& s);
private:
	char* _ptr;
};

ostream& operator<<(ostream& _cout, Mystring& s) {
	_cout << s._ptr;
	return _cout;
}



int main() {
	Mystring a("1324");
	Mystring b("abcd");
	Mystring c;

	c = a + b;

	cout << c << endl;

	return 0;
}

#include <iostream>
using namespace std;
double PI = 3.14156;

// round , Interface class 
class Circle {
public:
	// Surface area 
	virtual double area() = 0;
	// Volume 
	virtual double volume() = 0;

protected:
	// radius 
	double _r;
};

// The ball 
class Sphere :public Circle {
public:
	Sphere(double r = 0.0) {
		_r = r;
	}

	// Surface area 
	virtual double area() {
		return 4 * PI * _r * _r;
	}

	// Volume 
	virtual double volume() {
		return 4.0/3 * PI * _r * _r * _r;
	}
};

// Cylinder 
class Column :public Circle {
public:
	Column(double r = 0, double h = 0) {
		_r = r;
		_h = h;
	}

	// Surface area 
	virtual double area() {
		return 2 * (PI * _r * _r) + (PI * 2 * _r * _h);
	}

	// Volume 
	virtual double volume() {
		return PI * _r * _r * _h;
	}

private:
	// high 
	double _h;
};


int main() {
	double rS, rC, h;

	cout << " Please enter the radius of the sphere ：";
	cin >> rS;

	cout << " Please enter the radius of the cylinder ：";
	cin >> rC;

	cout << " Please enter the height of the cylinder ：";
	cin >> h;

	cout << endl;

	Sphere sphere(rS);
	Column column(rC, h);

	cout << " The radius of the sphere is ：" << rS << endl;
	cout << " The surface area of the sphere is ：" << sphere.area() << endl;
	cout << " The volume of the sphere is ：" << sphere.volume() << endl << endl;
	
	cout << " The radius of the cylinder is ：" << rC << endl;
	cout << " The surface area of the cylinder is ：" << column.area() << endl;
	cout << " The volume of the cylinder is ：" << column.volume() << endl << endl;

	return 0;
}