1，定义一个Mystring类代替string的功能

#include <iostream>
#include <string.h>using namespace std;
class Mystring
{friend ostream &operator<<(ostream &cout,const Mystring &s);friend istream &operator>>(istream &cin,Mystring &s);
private:char *str;
public:Mystring(char *str=nullptr){this->str = new char[sizeof(str)];strcpy(this->str,str);}Mystring(const Mystring &other){str = new char[sizeof(other.str)];strcpy(str,other.str);}Mystring &operator=(const Mystring &s){str = new char[sizeof(s.str)];str = s.str;return *this;}~Mystring(){delete []str;}Mystring &operator=( char *s){str = s;return *this;}long size(){return strlen(str);}Mystring operator+(const Mystring &s) const{Mystring temp = *this;strcat(temp.str,s.str);return temp;}bool operator>(const Mystring &s)const{if(strcmp(str,s.str)>0){return true;}else{return false;}}bool operator==(const Mystring &s)const{if(strcmp(str,s.str)==0){return true;}else{return false;}}bool operator<(const Mystring &s)const{if(strcmp(str,s.str)<0){return true;}else{return false;}}void show(){cout << str << endl;}};
ostream &operator<<(ostream &cout,const Mystring &s)
{cout << s.str << endl;return cout;}
istream &operator>>(istream &cin,Mystring &s)
{cout << "please input:";cin >> s.str;return cin;
}int main()
{char buf[100]="123456";Mystring s1(buf);s1.show();Mystring s2 = s1;s2.show();Mystring s3 = s1+s2;s3.show();if(s1>s3){cout << "s1>s3"<<endl;}if(s1==s3){cout << "s1=s3" << endl;}else{cout << "s1<s3" << endl;}cin >> s3;cout << s3;return 0;
}

2，借书的类

#include <iostream>
#include <vector>using namespace std;
class Book
{friend void add_book(vector<Book> &v);friend istream &operator>>(istream &cin,Book &b);friend void borrow_book(vector<Book> &v);friend ostream &operator<<(ostream &cout,Book &b);friend void back_book(vector<Book> &v);
private:string book;string name;static int count;
public:Book(){}Book(string book,string name):book(book),name(name){}};
int Book::count=0;
istream &operator>>(istream &cin,Book &b)
{cout << "input book ,name:" << endl;cin >> b.book >> b.name ;return cin;
}
ostream &operator<<(ostream &cout,Book &b)
{cout << b.book << " " << b.name;return cout;
}void add_book(vector<Book> &v)
{Book b;cin >> b;v.push_back(b);b.count++;}
void borrow_book(vector<Book> &v)
{string a;cout << "book name:";cin >> a;for(int i=0;i<Book::count;i++){if(a==v[i].book){Book::count--;v.erase(v.begin()+i);}}cout << "not found" << endl;}
void back_book(vector<Book> &v)
{Book b;cin >> b;v.push_back(b);}
void show(vector<Book> &v)
{for(Book b:v){cout << b << endl;}}int main()
{vector<Book> v;while(1){cout << "add:1" << endl;cout << "borrow:2" << endl;cout << "check:3" << endl;cout << "back:4" << endl;cout << "exit:0" << endl;int flag;cin >> flag;switch (flag){case 1:add_book(v);break;case 2:borrow_book(v);break;case 3:show(v);break;case 4:back_book(v);break;case 0:return 0;}}return 0;
}

3，登陆界面设置