C++实验四 运算符重载和虚函数_.对于类mystring,要求重载‘+’运算符后可以计算表达式:a=b+c;表示两个字符串

内容提要

1.对于类MyString,要求重载‘+’运算符后可以计算表达式:a=b+c;表示两个字符串连接。其中a,b,c都是类MyString的对象。
2.使用虚函数编写程序求球体和圆柱体的体积及表面积。由于球体和圆柱体都可以看作由圆继承而来，所以可以定义圆类Circle作为基类。在Circle类中定义一个数据成员radius和两个虚函数area()和volume()。由Circle类派生Sphere类和Column类。在派生类中对虚函数area()和volume()重新定义，分别求球体和圆柱体的体积及表面积。

基本要求

重载相应的运算符并编写程序，能运用虚函数编写程序测试并提交程序。

源程序及运行结果

#include <iostream>
#include <cstring>
#define N 32
 
using namespace std;
 
class MyString
{
	char *d;
	int len;
public:
	MyString() { d = new char[N]; len = 0; }
	MyString(const char* a);
	MyString& operator + (MyString & a);
	MyString& operator + (char * a);
	MyString& operator + (const char *a);
 
	MyString& operator = (MyString & a);
	MyString& operator = (char * a);
	MyString& operator = (const char *a);
 
	int strLen(void) { return len; }
	char * D(void) { return d; }
	friend ostream & operator << (ostream &os, MyString &a);
};
 
MyString::MyString(const char *a)
{
	d = new char[strlen(a) + 1];
	strcpy(d, a);
	len = strlen(a);
}
 
MyString& MyString::operator + (MyString & a)
{
	if (len + a.strLen() > (N - 1))
	{
		char *tmp = new char[len + a.strLen() + 1];
		strcpy(tmp, d);
		strcat(tmp, a.D());
		d = tmp;
	}
	else
	{
		strcat(d, a.D());
	}
	len += a.strLen();
	return *this;
}
 
MyString& MyString::operator + (char * a)
{
	if (len + strlen(a) > (N - 1))
	{
		char *tmp = new char[len + strlen(a) + 1];
		strcpy(tmp, d);
		strcat(tmp, a);
		d = tmp;
	}
	else
	{
		strcat(d, a);
	}
	len += strlen(a);
	return *this;
}
 
MyString& MyString::operator + (const char *a)
{
	if (len + strlen(a) > (N - 1))
	{
		char *tmp = new char[len + strlen(a) + 1];
		strcpy(tmp, d);
		strcat(tmp, a);
		d = tmp;
	}
	else
	{
		strcat(d, a);
	}
	len += strlen(a);
	return *this;
}
 
MyString& MyString::operator = (MyString & a)
{
	if (&a != this && len > 0 && len < a.strLen())
	{
		delete[] d;
		d = new char[a.strLen() + 1];
	}
	strcpy(d, a.D());
	len = a.strLen();
	return *this;
}
 
MyString& MyString::operator = (char * a)
{
	if (d != NULL && len < strlen(a))
	{
		delete[] d;
		d = new char[strlen(a) + 1];
	}
	strcpy(d, a);
	len = strlen(a);
	return *this;
}
 
 
 
MyString& MyString::operator = (const char *a)
{
	if (d != NULL && len < strlen(a))
	{
		delete[] d;
		d = new char[strlen(a) + 1];
	}
	strcpy(d, a);
	len = strlen(a);
	return *this;
}
 
ostream & operator << (ostream &os, MyString &a)
{
	os << a.D();
	return os;
}
 
 
 
int main(void)
{
	MyString str("我从海边来 ");
	str = str + "深蓝的是天";
	cout << str << endl;
 
	str = str + " 浅蓝的是水 灰蓝的是海岸线";
	cout << str << endl;
 
	return 0;
}
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#include <iostream>
#define P 3.1415
using namespace std;
 
class Circle
{
	protected:
		double radius;
	public:
		virtual double area(void) = 0;
		virtual double volume(void) = 0;
};
 
class Sphere :public Circle
{
	public:
		Sphere(double r = 0) { radius = r; }
		virtual double area(void)
		{
			return 4.0 * P * radius * radius;
		}
		virtual double volume(void)
		{
			return (4.0 / 3.0) * P * radius * radius * radius;
		}
};
 
class Column :public Circle
{
	private:
		double high;
	public:
		Column(double r = 0, double h = 0) { radius = r; high = h; }
		virtual double area(void)
		{
			if (0 == high)
			{
				return P * radius * radius;
			}
			return 2.0* P * radius * radius + P * 2.0 * radius * high;
		}
		virtual double volume(void)
		{
			if (0 == high)
			{
				return 0;
			}
		return P * radius * radius * high;
		}
};
 
int main(void)
{
	double rS, rC, h;
	while (1)
	{
		cout << "请输入球体的半径：";
		cin >> rS;
		if (rS <= 0)
		{
			cout << "数据错误！\n\n";
		}
		else
			break;
	}
 
	while (1)
	{
		cout << "请输入圆柱体的半径：";
		cin >> rC;
		if (rC <= 0)
		{
			cout << "数据错误！\n\n";
		}
		else
			break;
	}
 
	while (1)
	{
		cout << "请输入圆柱体的高：";
		cin >> h;
		if (h <= 0)
		{
			cout << "数据错误！\n\n";
		}
		else
			break;
	}
 
	Sphere sphere(rS);
	Column column(rC, h);
	cout << "球体的半径为：" << rS << endl
		 << "球体的表面积为：" << sphere.area() << endl
		 << "球体的体积为：" << sphere.volume() << endl << endl;
	cout << "圆柱体的半径为：" << rC << endl
		 << "圆柱体的表面积为：" << column.area() << endl
	 	<< "圆柱体的体积为：" << column.volume() << endl << endl;
 
	return 0;
}
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