本博客内容为中国大学生MOOC国家精品课程《计算机程序设计C++》作业记录，仅供参考，观者忌照搬照抄，欢迎交流批评指正！
##第十二周编程作业
本周作业内容C++中的多态性
- 虚函数实现多态性
#include <iostream>
using namespace std;
class Pet
{
public:
virtual void Speak()
{
cout << "How does a pet speak?";
}
};
class Cat :public Pet
{
public:
void Speak()
{
cout << "miao!miao!";
}
};
class Dog :public Pet
{
public:
void Speak()
{
cout << "wang!wang!";
}
};
int main()
{
Pet p, *pet;
Cat c;
Dog d;
pet = &p;
pet->Speak(); cout << endl;
pet = &c;
pet->Speak(); cout << endl;
pet = &d;
pet->Speak(); cout << endl;
return 0;
}
- 抽象宠物类的实现
#include <iostream>
#include <string.h>
using namespace std;
class Pet
{
private:
char name[20];
int age;
char color[20];
public:
Pet(char *n="xxx", int age=0, char *c="xxx"){ strcpy(name, n); this->age = age;; strcpy(color, c); }
char *getname(){ return name; }
int getage(){ return age; }
char *getcolor(){ return color; }
virtual void Speak() = 0;
virtual void GetInfo() = 0;
};
class Cat :public Pet
{
public:
Cat(char *n = "xxx", int age = 0, char *c = "xxx") :Pet(n, age, c){};
void GetInfo()
{
cout << "猫的名字:" << getname() << endl;
cout << "猫的年龄:" << getage() << endl;
cout << "猫的颜色:" << getcolor() << endl;
}
void Speak()
{
cout << "猫的叫声:miao!miao!" << endl;
}
};
class Dog :public Pet
{
public:
Dog(char *n = "xxx", int age = 0, char *c = "xxx") : Pet(n, age, c){};
void GetInfo()
{
cout << "狗的名字:" << getname() << endl;
cout << "狗的年龄:" << getage() << endl;
cout << "狗的颜色:" << getcolor() << endl;
}
void Speak()
{
cout << "狗的叫声:wang!wang!" << endl;
}
};
int main()
{
Pet *pet;
char name[20], color[20];
int age;
cin >> name >> age >> color;
Cat c(name,age,color);
cin >> name >> age >> color;
Dog d(name,age,color);
pet = &c;
pet->GetInfo();
pet->Speak();
pet = &d;
pet->GetInfo();
pet->Speak();
return 0;
}
- 重载加法运算符的复数运算
#include <iostream>
using namespace std;
class Complex
{
private:
double real, imag;
public:
Complex(double a = 0, double b = 0) :real(a), imag(b){};
double Real(){ return real; }
double Imag(){ return imag; }
void set(double a, double b){ real = a; imag = b; }
Complex operator +(Complex);
friend ostream &operator <<(ostream &out,const Complex &a);//友元函数
};
Complex Complex::operator +(Complex a)
{
Complex temp;
temp.real = real + a.real;
temp.imag = imag + a.imag;
return temp;
}
ostream & operator <<(ostream &out,const Complex &a)
{
out << a.real << "+j" << a.imag;
return out;
}
int main()
{
double real1,imag1,real2,imag2;
cin >> real1 >> imag1;
cin >> real2 >> imag2;
Complex a(real1, imag1), b(real2, imag2);
cout << a << endl;
cout << b << endl;
cout << a + b << endl;
return 0;
}
此处要对<<运算符进行重载，需要使用友元函数，代码格式如下
//类内需要关键字 friend
friend ostream &operator <<(ostream &out,const Classname &a);
//类外
ostream & operator <<(ostream &out,const Classname &a)
{...}
- 重载矩阵加法运算
#include <iostream>
using namespace std;
class Matrix
{
private:
int row, column;
int **M;
public:
Matrix(int r = 0, int c = 0, int **m = NULL)
{
row = r;
column = c;
M = m;
}
Matrix operator +(Matrix);
int get(int i, int j){ return M[i][j]; }
bool ifnull()//判断矩阵是否为空
{
if (M != NULL) return true;
else return false;
}
friend ostream &operator <<(ostream &out, const Matrix &a);
};
Matrix Matrix::operator+(Matrix a)
{
Matrix temp;
temp.row = a.row;
temp.column = a.column;
temp.M = new int*[row];
for (int i = 0; i < row; i++)
{
temp.M[i] = new int[column];
for (int j = 0; j < column; j++)
{
temp.M[i][j] = M[i][j] + a.M[i][j];
}
}
return temp;
}
ostream &operator<<(ostream &out, const Matrix &a)
{
for (int i = 0; i < a.row; i++)
{
int j = 0;
for (j = 0; j < a.column - 1; j++)
{
cout << a.M[i][j] << ' ';
}
cout << a.M[i][j] << endl;
}
return out;
}
int main()
{
int row, column;
int **m1,**m2;
cin >> row >> column;
m1 = new int*[row];
for (int i = 0; i < row; i++)
{
m1[i] = new int[column];
for (int j = 0; j < column; j++)
{
cin >> m1[i][j];
}
}
m2 = new int*[row];
for (int i = 0; i < row; i++)
{
m2[i] = new int[column];
for (int j = 0; j < column; j++)
{
cin >> m2[i][j];
}
}
Matrix matrix1(row, column, m1), matrix2(row, column, m2), matrix3;
matrix3 = matrix1 + matrix2;
cout << matrix3;
return 0;
}
此程序使用了动态二维数组
- 纯虚函数与基类指针数组的应用
#include <iostream>
using namespace std;
const double PI = 3.14159;
class Shape
{
public:
virtual void printName() = 0;
virtual double printArea() = 0;
};
class Circle :public Shape
{
private:
double r;
public:
Circle(double r = 0){ this->r = r; }
void printName()
{
cout << "圆:半径=" << r;
}
double printArea()
{
cout << "面积:" << PI * r * r;
return PI * r * r;
}
};
class Square :public Shape
{
public:
double l;
public:
Square(double l = 0){ this->l = l; }
void printName()
{
cout << "正方形:边长=" << l;
}
double printArea()
{
cout << "面积:" << l*l;
return l*l;
}
};
class Rectangle :public Shape
{
public:
double width,lengh;
public:
Rectangle(double l = 0, double w = 0){ lengh = l; width = w; }
void printName()
{
cout << "长方形:长="<< lengh<<",宽="<< width;
}
double printArea()
{
cout << "面积:" << width*lengh;
return width*lengh;
}
};
class Trapezoid :public Shape
{
public:
double up, down, height;
public:
Trapezoid(double u = 0, double d = 0, double h = 0){ up = u; down = d; height = h; }
void printName()
{
cout << "梯形:上底=" << up << ",下底=" << down << ",高=" << height;
}
double printArea()
{
cout << "面积:" << (up+down)*height/2;
return (up + down)*height / 2;
}
};
class Triangle :public Shape
{
public:
double h, l;
public:
Triangle(double l = 0, double h = 0){ this->l = l; this->h = h; }
void printName()
{
cout << "三角形:底边=" << l << ",高=" << h;
}
double printArea()
{
cout << "面积:" << h*l/2;
return h*l / 2;
}
};
int main()
{
double r, L, l, w, u, p, h, down, height, area=0;
cin >> r >> L >> l >> w >> u >> p >> h >> down >> height;
Circle a(r); Square b(L); Rectangle d(l, w); Trapezoid e(u, p, h); Triangle f(down, height);
Shape *s;
s = &a; s->printName(); cout << ','; area += s->printArea(); cout << endl;
s = &b; s->printName(); cout << ','; area += s->printArea(); cout << endl;
s = &d; s->printName(); cout << ','; area += s->printArea(); cout << endl;
s = &e; s->printName(); cout << ','; area += s->printArea(); cout << endl;
s = &f; s->printName(); cout << ','; area += s->printArea(); cout << endl;
cout << "总面积:" << area << endl;
return 0;
}
以上为第十二周的编程作业。