c++ primer plus 习题答案(6)

p425.1

 1 #include<iostream>

 2 #include<cstring>

 3 #include<cstdlib>

 4 using namespace std;

 5 

 6 class Cow{

 7     char name[20];

 8     char *hobby;

 9     double weight;

10 public:

11     Cow();

12     Cow(const char *nm, const char *ho, double wt);

13     Cow(const Cow &c);

14     ~Cow();

15     Cow &operator=(const Cow &c);

16     void ShowCow()const;

17 };

18 

19 Cow::Cow(){

20     strcpy(name, "no body");

21     hobby = "nothing";

22     weight = 0.0;

23 }

24 

25 Cow::Cow(const char *nm, const char *ho, double wt){

26     std::strncpy(name, nm, 20);

27     hobby = new char[strlen(ho) + 1];

28     strcpy(hobby, ho);

29     weight = wt;

30 }

31 

32 Cow::Cow(const Cow &c){

33     hobby = new char[strlen(c.hobby) + 1];

34     strcpy(hobby, c.hobby);

35     strcpy(name, c.name);

36     weight = c.weight;

37 }

38 

39 Cow::~Cow(){

40     delete[]hobby;

41 }

42 

43 Cow & Cow::operator=(const Cow &c){

44     if (this == &c)

45         return *this;

46     delete[]hobby;

47     hobby = new char[strlen(c.hobby) + 1];

48     strcpy(hobby, c.hobby);

49     strcpy(name, c.name);

50     weight = c.weight;

51     cout << "hobby " << hobby << endl

52         << "name " << name << endl

53         << "weight " << weight << endl;

54     return *this;

55 }

56 

57 void Cow::ShowCow()const{

58     std::cout << "name is " << name << std::endl

59         << "hobby is " << hobby << std::endl

60         << "weight is " << weight << std::endl;

61 }

62 

63 int main(){

64     Cow test1, test2("Max", "soccer", 6.7);

65     test1.ShowCow();

66     test2.ShowCow();

67     Cow test3("Stack", "vollyball", 3.45);

68     cin.get();

69     test1 = test3;

70     test1.ShowCow();

71 

72     system("pause");

73     return 0;

74 }

p426.3

  1 //头文件：

  2 #include<iostream>

  3 #include<string>

  4 using std::istream;

  5 using std::ostream;

  6 

  7 #ifndef STRING2_H_

  8 #define STRING2_H_

  9 class String{

 10 private:

 11     char *str;

 12     int len;

 13     static int num_strings;

 14     static const int CINIM = 80;

 15 public:

 16     String(const char *s);

 17     String();

 18     String(const String &);

 19     ~String();

 20     int length()const { return len; }

 21     String & operator=(const String &);

 22     String &operator=(const char*);

 23     char&operator[](int i);

 24     const char &operator[](int i)const;

 25     String & Stringlow();

 26     char * Stringup();

 27     int has(char);

 28     friend char * operator+(const String &st1, const String &st2);

 29     friend bool operator<(const String &st1, const String &st2);

 30     friend bool operator==(const String &st1, const String &st2);

 31     friend ostream &operator<<(ostream &os, const String &st);

 32     friend istream &operator>>(istream &is, String &st);

 33     static int howmany();

 34 };

 35 

 36 #endif

 37 

 38 //方法：

 39 #include<iostream>

 40 #include<cctype>

 41 #include<cstring>

 42 #include<string>

 43 #include"String2.h"

 44 

 45 using std::cin;

 46 using std::cout;

 47 using std::endl;

 48 

 49 int String::num_strings = 0;

 50 

 51 String::String(const char *s){

 52     num_strings++;

 53     len = strlen(s);

 54     str = new char[len+1];

 55     strcpy(str, s);

 56     cout << "num_strings " << num_strings << endl;

 57 }

 58 

 59 String::String(){

 60     num_strings++;

 61     len = 0;

 62     str = NULL;

 63     cout << "num_strings " << num_strings << endl;

 64 }

 65 

 66 String::String(const String &st){

 67     num_strings++;

 68     len = st.len;

 69     str = new char[len + 1];

 70     strcpy(str, st.str);

 71     cout << "num_strings " << num_strings << endl;

 72 }

 73 

 74 String::~String(){

 75     num_strings--;

 76     delete[]str;

 77     cout << "num_strings " << num_strings << endl;

 78 }

 79 

 80 String & String::operator=(const String &st){

 81     if (&st == this)

 82         return *this;

 83     delete[]str;

 84     len = st.len;

 85     str = new char[len + 1];

 86     strcpy(str, st.str);

 87     return *this;

 88 }

 89 

 90 String & String::operator=(const char*s){

 91     delete[]str;

 92     len = strlen(s);

 93     str = new char[len + 1];

 94     strcpy(str, s);

 95     return *this;

 96 }

 97 

 98 char & String::operator[](int i){

 99     return str[i];

100 }

101 

102 const char & String::operator[](int i)const{

103     return str[i];

104 }

105 

106 String & String::Stringlow(){

107     for (int i = 0; i < len; i++)

108         str[i] = tolower(str[i]);

109     return *this;

110 }

111 

112 char * String::Stringup(){

113     for (int i = 0; i < len; i++)

114         str[i] = toupper(str[i]);

115     return str;

116 }

117 

118 int String::has(char ch){

119     int count = 0;

120     for (int i = 0; i < len; i++)

121         if (str[i] == ch)

122             count++;

123     return count;

124 }

125 

126 char * operator+(const String &st1, const String &st2){

127     char *st3 = new char[st1.len + st2.len+2];

128     for (int i = 0; i < st1.len; i++)

129         st3[i] = st1[i];

130     for (int j = 0; j < st2.len; j++)

131         st3[st1.len +1+ j] = st2[j];

132     st3[st1.len] = ' ';

133     st3[st1.len + st2.len + 1] = '\0';

134     return st3;

135 }

136 

137 bool operator<(const String &st1, const String &st2){

138     if (strcmp(st1.str, st2.str))

139         return false;

140     else return true;

141 }

142 

143 bool operator==(const String &st1, const String &st2){

144     if (strcmp(st1.str, st2.str) == 0)

145         return true;

146     else return false;

147 }

148 

149 ostream &operator<<(ostream &os, const String &st){

150     os << "str: " << st.str << endl;

151     return os;

152 }

153 

154 istream &operator>>(istream &is, String &st){

155     char temp[String::CINIM];

156     is.get(temp, String::CINIM);

157     if (is)

158         st = temp;

159     while (is&&is.get() != '\n')

160         continue;

161     return is;

162 }

163 

164 int String::howmany(){

165     return num_strings;

166 }

167 

168 //驱动：

169 #include<iostream>

170 #include<cstdlib>

171 using namespace std;

172 #include "string2.h"

173 

174 int main(){

175     String s1(" and i am a C++ student. ");

176     String s2 = "please enter your name: ";

177     String s3;

178     cout << s2;

179     cin >> s3;

180     s2 = "my name is " + s3;

181     cout << s2 << ".\n";

182     s2 = s2 + s1;

183     s2.Stringup();

184     cout << "the string\n" << s2 << "\ncontains " <<

185         s2.has('A') << "'A' characters in it.\n";

186     s1 = "red";

187     String rgb[3] = { String(s1), String(" green"), String("blue") };

188     cout << "enter the name of a primary color for mixing light: ";

189     String ans;

190     bool success = false;

191     while (cin >> ans){

192         ans.Stringlow();

193         for (int i = 0; i < 3; i++){

194             if (ans == rgb[i]){

195                 cout << "that's right!\n";

196                 success = true;

197                 break;

198             }

199         }

200         if (success)

201             break;

202         else

203             cout << "try again\n";

204     }

205     cout << "bye\n";

206     system("pause");

207     return 0;

208 }