c++ primer plus 习题答案(6)

p425.1

 #include<iostream>
 #include<cstring>
 #include<cstdlib>
 using namespace std;

 class Cow{
     char name[];
     char *hobby;
     double weight;
 public:
     Cow();
     Cow(const char *nm, const char *ho, double wt);
     Cow(const Cow &c);
     ~Cow();
     Cow &operator=(const Cow &c);
     void ShowCow()const;
 };

 Cow::Cow(){
     strcpy(name, "no body");
     hobby = "nothing";
     weight = 0.0;
 }

 Cow::Cow(const char *nm, const char *ho, double wt){
     std::strncpy(name, nm, );
     hobby = new char[strlen(ho) + ];
     strcpy(hobby, ho);
     weight = wt;
 }

 Cow::Cow(const Cow &c){
     hobby = new char[strlen(c.hobby) + ];
     strcpy(hobby, c.hobby);
     strcpy(name, c.name);
     weight = c.weight;
 }

 Cow::~Cow(){
     delete[]hobby;
 }

 Cow & Cow::operator=(const Cow &c){
     if (this == &c)
         return *this;
     delete[]hobby;
     hobby = new char[strlen(c.hobby) + ];
     strcpy(hobby, c.hobby);
     strcpy(name, c.name);
     weight = c.weight;
     cout << "hobby " << hobby << endl
         << "name " << name << endl
         << "weight " << weight << endl;
     return *this;
 }

 void Cow::ShowCow()const{
     std::cout << "name is " << name << std::endl
         << "hobby is " << hobby << std::endl
         << "weight is " << weight << std::endl;
 }

 int main(){
     Cow test1, test2("Max", "soccer", 6.7);
     test1.ShowCow();
     test2.ShowCow();
     Cow test3("Stack", "vollyball", 3.45);
     cin.get();
     test1 = test3;
     test1.ShowCow();

     system("pause");
     return ;
 }

p426.3

 //头文件：
 #include<iostream>
 #include<string>
 using std::istream;
 using std::ostream;

 #ifndef STRING2_H_
 #define STRING2_H_
 class String{
 private:
     char *str;
     int len;
     static int num_strings;
     static const int CINIM = ;
 public:
     String(const char *s);
     String();
     String(const String &);
     ~String();
     int length()const { return len; }
     String & operator=(const String &);
     String &operator=(const char*);
     char&operator[](int i);
     const char &operator[](int i)const;
     String & Stringlow();
     char * Stringup();
     int has(char);
     friend char * operator+(const String &st1, const String &st2);
     friend bool operator<(const String &st1, const String &st2);
     friend bool operator==(const String &st1, const String &st2);
     friend ostream &operator<<(ostream &os, const String &st);
     friend istream &operator>>(istream &is, String &st);
     static int howmany();
 };

 #endif

 //方法：
 #include<iostream>
 #include<cctype>
 #include<cstring>
 #include<string>
 #include"String2.h"

 using std::cin;
 using std::cout;
 using std::endl;

 int String::num_strings = ;

 String::String(const char *s){
     num_strings++;
     len = strlen(s);
     str = new char[len+];
     strcpy(str, s);
     cout << "num_strings " << num_strings << endl;
 }

 String::String(){
     num_strings++;
     len = ;
     str = NULL;
     cout << "num_strings " << num_strings << endl;
 }

 String::String(const String &st){
     num_strings++;
     len = st.len;
     str = new char[len + ];
     strcpy(str, st.str);
     cout << "num_strings " << num_strings << endl;
 }

 String::~String(){
     num_strings--;
     delete[]str;
     cout << "num_strings " << num_strings << endl;
 }

 String & String::operator=(const String &st){
     if (&st == this)
         return *this;
     delete[]str;
     len = st.len;
     str = new char[len + ];
     strcpy(str, st.str);
     return *this;
 }

 String & String::operator=(const char*s){
     delete[]str;
     len = strlen(s);
     str = new char[len + ];
     strcpy(str, s);
     return *this;
 }

 char & String::operator[](int i){
     return str[i];
 }

 const char & String::operator[](int i)const{
     return str[i];
 }

 String & String::Stringlow(){
     for (int i = ; i < len; i++)
         str[i] = tolower(str[i]);
     return *this;
 }

 char * String::Stringup(){
     for (int i = ; i < len; i++)
         str[i] = toupper(str[i]);
     return str;
 }

 int String::has(char ch){
     int count = ;
     for (int i = ; i < len; i++)
         if (str[i] == ch)
             count++;
     return count;
 }

 char * operator+(const String &st1, const String &st2){
     char *st3 = new char[st1.len + st2.len+];
     for (int i = ; i < st1.len; i++)
         st3[i] = st1[i];
     for (int j = ; j < st2.len; j++)
         st3[st1.len ++ j] = st2[j];
     st3[st1.len] = ' ';
     st3[st1.len + st2.len + ] = '\0';
     return st3;
 }

 bool operator<(const String &st1, const String &st2){
     if (strcmp(st1.str, st2.str))
         return false;
     else return true;
 }

 bool operator==(const String &st1, const String &st2){
     if (strcmp(st1.str, st2.str) == )
         return true;
     else return false;
 }

 ostream &operator<<(ostream &os, const String &st){
     os << "str: " << st.str << endl;
     return os;
 }

 istream &operator>>(istream &is, String &st){
     char temp[String::CINIM];
     is.get(temp, String::CINIM);
     if (is)
         st = temp;
     while (is&&is.get() != '\n')
         continue;
     return is;
 }

 int String::howmany(){
     return num_strings;
 }

 //驱动：
 #include<iostream>
 #include<cstdlib>
 using namespace std;
 #include "string2.h"

 int main(){
     String s1(" and i am a C++ student. ");
     String s2 = "please enter your name: ";
     String s3;
     cout << s2;
     cin >> s3;
     s2 = "my name is " + s3;
     cout << s2 << ".\n";
     s2 = s2 + s1;
     s2.Stringup();
     cout << "the string\n" << s2 << "\ncontains " <<
         s2.has('A') << "'A' characters in it.\n";
     s1 = "red";
     String rgb[] = { String(s1), String(" green"), String("blue") };
     cout << "enter the name of a primary color for mixing light: ";
     String ans;
     bool success = false;
     while (cin >> ans){
         ans.Stringlow();
         for (int i = ; i < ; i++){
             if (ans == rgb[i]){
                 cout << "that's right!\n";
                 success = true;
                 break;
             }
         }
         if (success)
             break;
         else
             cout << "try again\n";
     }
     cout << "bye\n";
     system("pause");
     return ;
 }