c++ primer plus 习题答案(6)

p425.1

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

class Cow{
    char name[20];
    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, 20);
    hobby = new char[strlen(ho) + 1];
    strcpy(hobby, ho);
    weight = wt;
}

Cow::Cow(const Cow &c){
    hobby = new char[strlen(c.hobby) + 1];
    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) + 1];
    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 0;
}

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 = 80;
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 = 0;

String::String(const char *s){
    num_strings++;
    len = strlen(s);
    str = new char[len+1];
    strcpy(str, s);
    cout << "num_strings " << num_strings << endl;
}

String::String(){
    num_strings++;
    len = 0;
    str = NULL;
    cout << "num_strings " << num_strings << endl;
}

String::String(const String &st){
    num_strings++;
    len = st.len;
    str = new char[len + 1];
    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 + 1];
    strcpy(str, st.str);
    return *this;
}

String & String::operator=(const char*s){
    delete[]str;
    len = strlen(s);
    str = new char[len + 1];
    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 = 0; i < len; i++)
        str[i] = tolower(str[i]);
    return *this;
}

char * String::Stringup(){
    for (int i = 0; i < len; i++)
        str[i] = toupper(str[i]);
    return str;
}

int String::has(char ch){
    int count = 0;
    for (int i = 0; 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+2];
    for (int i = 0; i < st1.len; i++)
        st3[i] = st1[i];
    for (int j = 0; j < st2.len; j++)
        st3[st1.len +1+ j] = st2[j];
    st3[st1.len] = ' ';
    st3[st1.len + st2.len + 1] = '';
    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) == 0)
        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() != '
')
        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 << ".
";
    s2 = s2 + s1;
    s2.Stringup();
    cout << "the string
" << s2 << "
contains " <<
        s2.has('A') << "'A' characters in it.
";
    s1 = "red";
    String rgb[3] = { 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 = 0; i < 3; i++){
            if (ans == rgb[i]){
                cout << "that's right!
";
                success = true;
                break;
            }
        }
        if (success)
            break;
        else
            cout << "try again
";
    }
    cout << "bye
";
    system("pause");
    return 0;
}