002:继承自string的MyString

描述
程序填空，输出指定结果

#include <cstdlib>
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
class MyString:public string
{
// 在此处补充你的代码
};


int main()
{
	MyString s1("abcd-"),s2,s3("efgh-"),s4(s1);
	MyString SArray[4] = {"big","me","about","take"};
	cout << "1. " << s1 << s2 << s3<< s4<< endl;
	s4 = s3;
	s3 = s1 + s3;
	cout << "2. " << s1 << endl;
	cout << "3. " << s2 << endl;
	cout << "4. " << s3 << endl;
	cout << "5. " << s4 << endl;
	cout << "6. " << s1[2] << endl;
	s2 = s1;
	s1 = "ijkl-";
	s1[2] = 'A' ;
	cout << "7. " << s2 << endl;
	cout << "8. " << s1 << endl;
	s1 += "mnop";
	cout << "9. " << s1 << endl;
	s4 = "qrst-" + s2;
	cout << "10. " << s4 << endl;
	s1 = s2 + s4 + " uvw " + "xyz";
	cout << "11. " << s1 << endl;
        sort(SArray,SArray+4);
	for( int i = 0;i < 4;i ++ )
	cout << SArray[i] << endl;
	//s1的从下标0开始长度为4的子串
	cout << s1(0,4) << endl;
	//s1的从下标5开始长度为10的子串
	cout << s1(5,10) << endl;
	return 0;
}

输入

无

输出

1. abcd-efgh-abcd-
2. abcd-
3.
4. abcd-efgh-
5. efgh-
6. c
7. abcd-
8. ijAl-
9. ijAl-mnop
10. qrst-abcd-
11. abcd-qrst-abcd- uvw xyz
about
big
me
take
abcd
qrst-abcd-

继承后需要构建的：
1.无参构造函数
2.有参构造函数
3.复制构造函数

// 在此处补充你的代码
	public:
	MyString():string(){};       
	//无参构造函数——调用string的无参构造函数 
	MyString(const char *s): string(s){};   
	//有参构造函数——调用string的有参构造函数 
	MyString(const string &s): string(s){};  
	//复制函数——调用string的复制函数 
	MyString operator()(int s,int l)    
	//重构（），需要调用substr函数 
	{
		return substr(s,l);      
		//用string中给的substr函数 
	}
	//能在string对象上操作的，都能在MyString对象上操作 
	//[]继承 
	//+继承 
	//=继承 
	//+=继承 
	//（）需要调用substr函数，故在MyString中也需要设置一下 
// 

004:编程填空：统计动物数量

描述
代码填空，使得程序能够自动统计当前各种动物的数量

#include <iostream>
using namespace std;
// 在此处补充你的代码
void print() {
	cout << Animal::number << " animals in the zoo, " << Dog::number << " of them are dogs, " << Cat::number << " of them are cats" << endl;
}

int main() {
	print();
	Dog d1, d2;
	Cat c1;
	print();
	Dog* d3 = new Dog();
	Animal* c2 = new Cat;
	Cat* c3 = new Cat;
	print();
	delete c3;
	delete c2;
	delete d3;
	print();
}

输入

无

输出

0 animals in the zoo, 0 of them are dogs, 0 of them are cats
3 animals in the zoo, 2 of them are dogs, 1 of them are cats
6 animals in the zoo, 3 of them are dogs, 3 of them are cats
3 animals in the zoo, 2 of them are dogs, 1 of them are cats

补充的代码
不用虚函数猫的数量不对，虚函数在之后的课程讲解。

class Animal{
public:
static int number;
	Animal(){          //调用构造函数，number++ 
		number++;
	}
	virtual~Animal(){        //调用析构函数，number-- 
		number--;
	}
};

class Dog:public Animal{     //派生类调用，也会调用基类 
public:
static int number;
	Dog(){
		number++;
	}
	~Dog(){
		number--;
	}
};

class Cat:public Animal{
public:
static int number;	
	Cat(){
		number++;
	}
	~Cat(){
		number--;
	}
};
int Dog::number=0;
int Animal::number=0;
int Cat::number=0;

全局中初始化静态变量的值，
要注明是基类还是派生类::