HW 7

俗话说的好：自闭从不单行，永远双至。果然这一场又自闭了。C语言没学好。。。。

Problem A: 字符串类（I）

main 函数：

int main()
{
    STR e;
    STR h("Hello World!");
    char s[100001];
    cout << e.length() << " ";
    e.putline();
    cout << h.length() << " ";
    h.putline();
    while(gets(s) != NULL)
    {
        STR str(s);
        cout << str.length() << " ";
        str.putline();
    }
}

怎么说那，本来以为RE到绝望了。。。。。，没想到还有B题。

总体来说还是水题，怎么说的怎么写吧。

AC代码：

#include <bits/stdc++.h>
using namespace std;
class STR
{
    char *p;
    int len;
public:
    STR():p(NULL),len(0){};
    STR(const char *s){len = strlen(s);p = new char[len+1];strcpy(p,s);};
    int length()
    {
        return len;
    }
    void putline()
    {
        if(p==NULL)
            cout << endl;
        else
        cout << p  << endl;
    }
    ~STR()
    {
        len = 0;
        if(p!=NULL)
            delete []p;
    }
};
int main()
{
    STR e;
    STR h("Hello World!");
    char s[100001];
    cout << e.length() << " ";
    e.putline();
    cout << h.length() << " ";
    h.putline();
    while(gets(s) != NULL)
    {
        STR str(s);
        cout << str.length() << " ";
        str.putline();
    }
}
 

Problem B: 字符串类（II）

main 函数：

int main()
{
    STR e;
    STR h("Hello World!");
    STR he = e + h;
    cout << he.length() << " ";
    he.putline();
    cout << e.length() << " ";
    e.putline();
    cout << h.length() << " ";
    h.putline();
    e += h;
    cout << e.length() << " ";
    e.putline();
    cout << h.length() << " ";
    h.putline();
 
    char s1[100001], s2[100001];
    while(gets(s1) != NULL && gets(s2) != NULL)
    {
        STR str1(s1), str2(s2);
        STR str = str1 + str2;
        cout << str.length() << " ";
        str.putline();
        cout << str1.length() << " ";
        str1.putline();
        cout << str2.length() << " ";
        str2.putline();
        str2 += str1;
        cout << str2.length() << " ";
        str2.putline();
        cout << str1.length() << " ";
        str1.putline();
    }
}

这个题RE到自闭，分析原因应该是忘记老师之前讲过的指针悬空问题，对于+=函数没有返回引用，也没有写拷贝构造函数，导致指针悬空，在析构的时候发生了错误。

附博客（讲返回对象与引用区别的）：

https://www.cnblogs.com/JMLiu/p/7928425.html

AC代码1(不返回引用)：

#include <bits/stdc++.h>
using namespace std;
class STR
{
    char *p;
    int len;
    //static int num;
public:
    STR():p(NULL),len(0){};
    STR(const char *s){len = strlen(s);p = new char[len+1];strcpy(p,s); p[len] = '';};
    STR(const STR &b){len = strlen(b.p);p = new char[len+1];strcpy(p,b.p); p[len] = '';};
    int length()
    {
        return len;
    }
    void putline()
    {
        if(p==NULL)
            cout << endl;
        else
        cout << p  << endl;
    }
    STR operator + (const STR&b)
    {
        char *s ;
        s = new char[len+b.len+1];
        strcpy(s,p);
        strcat(s,b.p);
        return STR(s);
    }
    STR operator+=(const STR &b)
    {
       STR c = *this+b;
        p  = new char[c.len+1];
        len = c.len;
        strcpy(p,c.p);
        return *this;
    }
    ~STR()
    {
        cout << "s = " <<  p << endl;
        if(len!=0)
            delete []p;
        len = 0;

    }
};

AC2(返回引用)：

#include <bits/stdc++.h>
using namespace std;
class STR
{
    char *p;
    int len;
public:
    STR():p(NULL),len(0){};
    STR(const char *s){len = strlen(s);p = new char[len+1];strcpy(p,s); p[len] = '';};
    int length()
    {
        return len;
    }
    void putline()
    {
        if(p==NULL)
            cout << endl;
        else
        cout << p  << endl;
    }
    STR operator + (const STR&b)
    {
        char *s ;
        s = new char[len+b.len+1];
        int i = 0;
        for(i = 0;i<len;i++)
            s[i] = p[i];
        for(int j = 0 ;j<b.len;i++,j++)
            s[i] = b.p[j];
        s[i] = '';
        //cout << s << endl;
        return STR(s);
    }
    STR& operator+=(const STR &b)
    {
        STR c = *this+b;
        //cout << c.p << endl;
        p = new char [c.len+1];
        strcpy(p,c.p);
        //cout << p << endl;
        len = c.len;
        return *this;
    }
    ~STR()
    {
        if(len!=0)
            delete []p;
        len = 0;
 
    }
};

Problem C: 学生干部虚基类：

main 函数：

int main( )
{
    string name, major, post, addr, tel;
    int age;
    char sex;
    float wage;
    cin>>name>>age>>sex>>addr>>tel>>major>>post>>wage;
 
    Student_Cadre st_ca(name, age, sex,  addr, tel, major, post,wage);
    st_ca.display( );
 
    cout<<endl;
    string newAddr, newTel1, newTel2;
    cin>>newAddr>>newTel1>>newTel2;
 
    st_ca.setAddr(newAddr);
    st_ca.Student::setTel(newTel1);
    st_ca.Cadre::setTel(newTel2);
    st_ca.display( );
    return 0;
}

类的虚继承，打比方来说，类D继承于类B和类C，而类C和类B有相同的基类A，因此在类D中事实上存在两个类A的对象和方法，在类D中调用类A的对象或方法时，就会产生二义性，但如果采用虚拟继承，在这个继承的过程中，就只会产生一个类A的对象及方法，就不会产生二义性。

最后CE了两发，没想到竟然是万能头害的，major居然是个关键字，自闭。。。。

AC代码：

#include <iostream>
#include <string>
using namespace std;
class Person
{
    string name,addr,tel;
    int age;
    char sex;
    friend class Student_Cadre;
    friend class Student;
    friend class Cadre;
public:
    //Person(){};
    Person(string _name,int _age,char _sex,string _addr,string _tel):name(_name),sex(_sex),tel(_tel),addr(_addr),age(_age){};
    void setAddr(string _add){addr = _add;}
    void setTel(string _tel){tel = _tel;}
};
class Student:virtual public Person
{
    string major;
    friend class Student_Cadre;
public:
    //Student(){};
    Student(string _name,int _age,char _sex,string _addr,string _tel,string _major):Person(_name,_age,_sex,_addr,_tel),major(_major){};
};
class Cadre:virtual public Person
{
    string post;
    friend class Student_Cadre;
public:
   // Cadre(){};
    Cadre(string _name,int _age,char _sex,string _addr,string _tel,string _post):Person(_name,_age,_sex,_addr,_tel),post(_post){};
};
class Student_Cadre:public Student,public Cadre
{
    float wages;
public:
    Student_Cadre(string _name,int _age,char _sex,string _addr,string _tel,string _major,string _post,float _wages):Person(_name,_age,_sex,_addr,_tel),Student(_name,_age,_sex,_addr,_tel,_major),Cadre(_name,_age,_sex,_addr,_tel,_post),wages(_wages){};
    void display()
    {
        cout << "name:" << this->name << endl;
        cout << "age" << age << endl;
        cout << "sex:" << sex << endl;
        cout << "address:" << addr << endl;
        cout << "tel:" << tel << endl;
        cout << "major:" << major << endl;
        cout << "post:" << post << endl;
        cout << "wages:" << wages << endl;
    }
};

Problem D: 选举班干部了！

main 函数：

int main()
{
    int num;
    string name, position;
    bool sex;
    int grade;
    Student *header, *student, *curStudent;
 
    cin>>name>>sex>>grade>>position;
    header = new StudentCadre(name, sex, grade,position);
    curStudent = header;
    cin>>num;
    for (int i = 0; i < num; i++)
    {
        cin>>name>>sex>>grade;
        student = new Student(name, sex, grade);
        curStudent -> setNext(student);
        curStudent = curStudent -> getNext();
    }
    ((StudentCadre*)header) -> showInfo();
    cout<<endl;
    curStudent = header;
    while (curStudent -> getNext() != NULL)
    {
        curStudent = curStudent -> getNext();
        curStudent->showInfo();
        cout<<endl;
    }
 
    curStudent = header;
    while (curStudent != NULL)
    {
        student = curStudent;
        curStudent = curStudent -> getNext();
        delete student;
    }
    return 0;
}

继承水题：

#include <bits/stdc++.h>
using namespace std;
class Student
{
    string name;
    bool sex;
    int grade;
    Student *next;
    friend class StudentCadre;
public:
    Student(){};
    Student(string _name,bool _sex,int _grade):name(_name),sex(_sex),grade(_grade),next(NULL){cout << "A student named by " << name << " is created!" << endl;}
    Student(Student&b){name = b.name,sex = b.sex,grade = b.grade; *next = *(b.next);}
    void showInfo()
    {
        cout << "name = " << name <<", sex = " << sex << ", grade = "<< grade  << ";" ;
    }
    Student* getNext()
    {
        return next;
    }
    void setNext(Student *s)
    {
        next = s;
    }
    ~Student()
    {
        //delete next;
        cout << "A student named by " << name << " is erased." << endl;
    }
};
class  StudentCadre:public Student
{
    string postion;
public:
    //StudentCadre(){cout << 2 << endl;}
    StudentCadre(string _name, bool _sex, int _grade, string pos):Student(_name,_sex,_grade),postion(pos){cout << "A student cadre with position " << postion << " is created." << endl;};
    StudentCadre(StudentCadre &b)
    {
        name = b.name,sex = b.sex,grade = b.grade;
        postion = b.postion;
        *next = *(b.next);
    }
    void showInfo()
    {
        cout << "name = " << name <<", sex = " << sex << ", grade = "<< grade  << "; " << "position = " << postion << "." ;
    }
};

Problem E: 立体空间中的点（I）

main 函数：

int main()
{
    int cases;
    cin>>cases;
    for(int i = 1; i <= cases; i++)
    {
        double x, y, z;
        int point_type;
        cin>>point_type;
        if(point_type == 2)
        {
            cin>>x>>y;
            Point p(x, y);
            p.showPoint();
        }
        if(point_type == 3)
        {
            cin>>x>>y>>z;
            Point_3D p(x, y, z);
            p.showPoint();
        }
    }
}

继承水，但不用继承写也能过，事实上也没有多大差别，但还是放继承的代码吧：

#include <bits/stdc++.h>
using namespace std;
class Point
{
    double x,y;
    friend class Point_3D;
public:
    Point(){};
    Point(double _x,double _y):x(_x),y(_y){};
    void showPoint()
    {
        cout << "2D Point (" << x << "," << y << ")" << endl;
    }
};
class Point_3D:public Point
{
    double z;
public:
    Point_3D(){};
    Point_3D(double _x,double _y,double _z):Point(_x,_y),z(_z){};
    void showPoint()
    {
        cout << "3D Point (" << x << "," << y << "," << z << ")" << endl;
    }
};

Problem F: 立体空间中的点（II）

mian 函数：

int main()
{
    cout<<"Invariable test output :"<<endl;
    Point_3D p3d;
    p3d.setPoint(-100, 0, 100);
    p3d.showPoint();
    p3d.x(0);
    p3d.y(100);
    cout<<"Point ("<<p3d.x()<<","<<p3d.y()<<","<<p3d.z()<<")"<<endl;
    cout<<"
Test data output :"<<endl;
    int cases;
    cin>>cases;
    for(int i = 1; i <= cases; i++)
    {
        double x, y, z;
        int point_type;
        cin>>point_type;
        if(point_type == 2)
        {
            cin>>x>>y;
            Point p(x, y);
            p.showPoint();
        }
        if(point_type == 3)
        {
            cin>>x>>y>>z;
            Point_3D p(x, y, z);
            p.showPoint();
        }
    }
    cout<<"Number of 2D Points : "<<Point::showNumber() - Point_3D::showNumber()<<endl;
    cout<<"Number of 3D Points : "<<Point_3D::showNumber() - 1<<endl;
}

继承水：

AC代码：

#include <bits/stdc++.h>
using namespace std;
class Point
{
    double x1,y1;
    static int N_P;
    friend class Point_3D;
public:
    Point(){N_P++;};
    Point(double _x,double _y):x1(_x),y1(_y){N_P++;};
    void showPoint()
    {
        cout << "2D Point (" << x1 << "," << y1 << ")" << endl;
    }
    void x(double _x){x1 =_x;}
    void y(double _y){y1 = _y;}
    double x()
    {
        return x1;
    }
    double y()
    {
        return y1;
    }
    static int showNumber(){return N_P;}
};
class Point_3D:public Point
{
    double z1;
    static int N_P3;
public:
    Point_3D(){N_P3++;};
    Point_3D(double _x,double _y,double _z):Point(_x,_y),z1(_z){N_P3++;};
    double z()
    {
        return z1;
    }
    void z(double _z)
    {
        z1 = _z;
    }
    void setPoint(double _x,double _y,double _z)
    {
        x1 =_x;
        y1 = _y;
        z1 = _z;
    }
    static int showNumber()
    {
        return N_P3;
    }
 
    void showPoint()
    {
        cout << "3D Point (" << x1 << "," << y1 << "," << z1 << ")" << endl;
    }
};
int Point::N_P = 0;
int Point_3D::N_P3 = 0;