[C++ Primer Plus] 第4章、复合类型（一）程序清单—

[C++ Primer Plus] 第4章、复合类型（一）程序清单——指针new和delete

程序清单4.1

 1 #include<iostream>
 2 using namespace std;
 3 
 4 void main(){
 5     int yams[3];
 6     yams[0]=7;
 7     yams[1]=8;
 8     yams[2]=6;
 9     int yams_cost[3]={20,30,5}; 
10 
11     cout<<"Total yams="<<yams[0]+yams[1]+yams[2]<<endl;
12     cout<<"The package with "<<yams[1]<<" yams costs "<<yams_cost[1]<<" cents per yam"<<endl;
13     cout<<"Total costs="<<yams[0]*yams_cost[0]+yams[1]*yams_cost[1]+yams[2]*yams_cost[2]<<" cents"<<endl;
14 
15     cout<<"Size of yams array="<<sizeof(yams)<<" bytes"<<endl;
16     cout<<"Size of yams[0]="<<sizeof(yams[0])<<" bytes"<<endl;
17 
18     system("pause");
19 }

程序清单4.2

 1 #include<iostream>
 2 #include<cstring>//strlen(),c语言版为string.h
 3 using namespace std;
 4 
 5 void main(){
 6     const int size=15;
 7     char name1[size];//char占一个字节
 8     char name2[size]="C++owboy";
 9 
10     cout<<"I am "<<name2<<".What's your name?"<<endl;
11     cin>>name1;
12     cout<<"Well,"<<name1<<",your name has "<<strlen(name1)<<" letters and is stored in an array of "<<sizeof(name1)<<" bytes"<<endl;
13     cout<<"Your initial is "<<name1[0]<<endl;
14     name2[3]='';
15     cout<<"Here are the first 3 characters of my name:"<<name2<<endl;
16     system("pause");
17 }

程序清单4.3

 1 #include<iostream>
 2 using namespace std;
 3 
 4 void main(){
 5     const int size=15;
 6     char name[size];
 7     char dessert[size];
 8 
 9     cout<<"What's your name?"<<endl;
10     cin>>name;
11     cout<<"What's your favorate dessert?"<<endl;
12     cin>>dessert;
13     cout<<"I have some delicious "<<dessert<<" for you."<<endl;
14     system("pause");
15 }

注意：cin使用空白（空格、制表符和换行符）来确定字符串的结束位置，所以cin将Alise放在了name数组，将dreeb放在了dessert数组

为了解决这种问题，C++提供getline()和get()方法，如下所示：

程序清单4.4

 1 #include<iostream>
 2 using namespace std;
 3 
 4 void main(){
 5     const int size=15;
 6     char name[size];
 7     char dessert[size];
 8 
 9     cout<<"What's your name?"<<endl;
10     cin.getline(name,size);
11     cout<<"What's your favorate dessert?"<<endl;
12     cin.getline(dessert,size);
13     cout<<"I have some delicious "<<dessert<<" for you."<<endl;
14     system("pause");
15 }

程序清单4.6

 1 #include<iostream>
 2 using namespace std;
 3 
 4 void main(){
 5     cout<<"你房子哪一年修的?"<<endl;
 6     int year;
 7     cin>>year;
 8     cout<<"房子的地址?"<<endl;
 9     char address[80];
10     cin.getline(address,80);
11     cout<<"Year built:"<<year<<endl<<"Address:"<<address<<endl<<"Done!";
12     system("pause");
13 }

用户没有输入地址的机会，问题在于：cin读取年份后，将回车键生成的换行符留在了队列中，后面的cin.getline()看到换行符后，将认为是一个空行。解决如下：

　　cin>>year;

　　cin.get();

程序清单4.7(string和数组)

 1 #include<iostream>
 2 #include<string>
 3 using namespace std;
 4 
 5 void main(){
 6     char ch1[20];
 7     char ch2[20]="jaguar";
 8     string str1;
 9     string str2="panther";
10 
11     cout<<"enter a kind of feline:";
12     cin>>ch1;
13     cout<<"enter another kind of feline:";
14     cin>>str1;
15     cout<<"Here are some felines:
"<<ch1<<" "<<ch2<<" "<<str1<<" "<<str2<<endl;
16     cout<<"The third letter in "<<ch2<<" is "<<ch2[2]<<endl;
17     cout<<"The third letter in "<<str2<<" is "<<str2[2]<<endl;
18     system("pause");
19 }

程序清单4.8(string赋值、拼接和附加)

 1 #include<iostream>
 2 #include<string>
 3 using namespace std;
 4 
 5 void main(){
 6     string str="penguin";
 7     string str2,str3,str4;
 8 
 9     str2=str;
10     cout<<"str2="<<str2<<endl;
11     str3="buzzard";
12     cout<<"str3="<<str3<<endl;
13     str4=str+str3;
14     cout<<"str4="<<str4<<endl;
15     str+=str3;
16     cout<<"str="<<str<<endl;
17     str2+=" is cute!";
18     cout<<"str2="<<str2<<endl;
19     system("pause");
20 }

程序清单4.9（cstring）

 1 #include<iostream>
 2 #include<string>
 3 #include<cstring>//strcpy,strcat,strlen
 4 using namespace std;
 5 
 6 void main(){
 7     char ch1[20];
 8     char ch2[20]="jaguar";
 9     string str1;
10     string str2="panther";
11 
12     str1=str2;
13     strcpy(ch1,ch2);
14 
15     str1+=" paste";
16     strcat(ch1," juice");
17 
18     int len1=str1.size();
19     int len2=strlen(ch1);
20 
21     cout<<"the string "<<str1<<" contains "<<len1<<"  characters"<<endl;
22     cout<<"the string "<<ch1<<" contains "<<len2<<"  characters"<<endl;
23     
24     system("pause");
25 }

程序清单4.10

 1 #include<iostream>
 2 #include<string>
 3 #include<cstring>
 4 using namespace std;
 5 
 6 void main(){
 7     char ch[20];
 8     string str;
 9     
10     cout<<"Length of string in ch before input:"<<strlen(ch)<<endl;
11     cout<<"Length of string in str before input:"<<str.size()<<endl;
12     cout<<"Enter a line of text:"<<endl;
13     cin.getline(ch,20);
14     cout<<"You entered:"<<ch<<endl;
15     cout<<"Enter another line of text:"<<endl;
16     getline(cin,str);
17     cout<<"You entered:"<<str<<endl;
18     cout<<"Length of string in ch after input:"<<strlen(ch)<<endl;
19     cout<<"Length of string in str after input:"<<str.size()<<endl;
20     
21     system("pause");
22 }

注意：未初始化的数组内容未定，strlen（）从数组中的第一个元素开始计算字节数，直到遇到空字符。在本例中数组内并未有空字符，所以字节数甚至超过了数组长度；未初始化的string对象长度置0

程序清单4.11+4.12(结构体)

 1 #include<iostream>
 2 using namespace std;
 3 
 4 struct  table{
 5     char name[20];
 6     float volumn;
 7     double price;
 8 };
 9 
10 void main(){
11     table guest={"GG",1.88,29.99};
12     table pal={"AA",3.12,32.99};
13     cout<<"Expand your guest list with "<<guest.name<<" and "<<pal.name<<endl;
14     cout<<"You can have both for  $"<<guest.price+pal.price<<endl;
15 
16     cout<<"------------------------------"<<endl;
17 
18     table choice=guest;
19     cout<<"choice:"<<choice.name<<" for $"<<choice.price<<endl;
20     
21     system("pause");
22 }

程序清单4.13

 1 #include<iostream>
 2 using namespace std;
 3 
 4 struct  table{
 5     char name[20];
 6     float volumn;
 7     double price;
 8 };
 9 
10 void main(){
11     table guest[2]={
12         {"GG",1.88,29.99},
13         {"AA",3.12,32.99}
14     };
15     cout<<"The guests "<<guest[0].name<<" and "<<guest[1].name<<endl<<"have a combined volumn of "<<guest[0].volumn+guest[1].volumn<<" cubic feet"<<endl;
16     
17     system("pause");
18 }

程序清单4.17(指针：new)

 1 #include<iostream>
 2 using namespace std;
 3 
 4 void main(){
 5     int nights=1001;
 6     int *pt = new int;
 7     *pt = 999;
 8     double *pd = new double;
 9     *pd = 100000000000.1;
10 
11     cout << "nights value=" << nights << ":location " << &nights << endl;
12     cout << "int value=" <<*pt<< ":location " <<pt<< endl;
13     cout << "double value=" << *pd << ":location " << pd << endl;
14     cout << "location of pointer pd:" << &pd<< endl;
15 
16     cout << "size of pt=" <<sizeof(pt)<< endl;
17     cout << "size of *pt=" << sizeof(*pt) << endl;
18     cout << "size of pd=" << sizeof(pd) << endl;
19     cout << "size of *pd=" << sizeof(*pd) << endl;
20     
21     system("pause");
22 }

程序清单4.18(new完之后要delete)

 1 #include<iostream>
 2 using namespace std;
 3 
 4 void main() {
 5     double *p = new double[3];//使用new创建动态数组
 6     p[0] = 0.2;
 7     p[1] = 0.5;
 8     p[2] = 0.8;
 9     cout << "p[1]=" << p[1] << endl;
10     p++;
11     cout << "Now p[0]=" << p[0] << endl;
12     cout << "p[1]=" << p[1] << endl;
13     p--;
14     cout << "And now p[0]=" << p[0] << endl;
15     delete[] p;//回归初始位置释放内存
16     getchar();
17 }

程序清单4.19

 1 #include<iostream>
 2 using namespace std;
 3 
 4 void main() {
 5     double wages[3] = { 10000.0,20000.0, 30000.0 };
 6     short stacks[3] = { 3 ,  2, 1 };
 7     double * pw = wages;
 8     short * ps = &stacks[0];
 9 
10     cout << "pw=" << pw <<",*pw="<<*pw<< endl;
11     pw++;
12     cout << "Now,pw=" << pw << ",*pw=" << *pw << endl;
13     cout << "ps=" << ps << ",*ps=" << *ps << endl;
14     ps++;
15     cout << "Now,ps=" << ps << ",*ps=" << *ps << endl;
16 
17     cout << "stacks[0]=" << stacks[0] << ",stacks[1]=" << stacks[1] << endl;
18     cout << "*stacks=" << *stacks<< ",*(stacks+1)=" << *(stacks + 1) << endl;
19     cout << "sizeof(wages)=" << sizeof(wages)<< endl;
20     cout << "sizeof(pw)=" << sizeof(pw) << endl;
21 
22     getchar();
23 }

程序清单4.20

 1 #define _CRT_SECURE_NO_WARNINGS
 2 #include<iostream>
 3 #include<cstring>
 4 using namespace std;
 5 
 6 void main() {
 7     char animal[20] = "bear";
 8     const char * bird = "wren";
 9     char * ps;
10 
11     cout << animal <<" and "<< bird << endl;
12     cout << "Enter a kind of animal:";
13     cin >> animal;
14     ps = animal;
15     cout << "ps="<<ps<< endl;
16     cout << "Before using strcpy()： 
 ";
17     cout << animal << " at " << (int *)animal << endl;
18     cout << ps << " at " << (int *)ps << endl;
19 
20     ps = new char[strlen(animal) + 1];
21     strcpy(ps, animal);
22     cout << "After using strcpy()： 
 ";
23     cout << animal << " at " << (int *)animal << endl;
24     cout << ps << " at " << (int *)ps << endl;
25     delete[] ps;
26 
27     system("pause");
28 }

程序清单4.21

 1 #include<iostream>
 2 using namespace std;
 3 
 4 struct inflatable {
 5     char name[20];
 6     float volumn;
 7     double price;
 8 };
 9 
10 void main() {
11     inflatable *ps = new inflatable;
12 
13     cout <<"Enter name of inflatable item:";
14     cin.get(ps->name,20);
15     cout << "Enter volumn in cubic feet:";
16     cin>>(*ps).volumn;
17     cout << "Enter price:$";
18     cin >>ps->price;
19 
20     cout << "Name:" << (*ps).name<< endl;
21     cout << "Volumn:" <<ps->volumn<< endl;
22     cout << "Price:" <<ps->price<< endl;
23     delete ps;
24 
25     system("pause");
26 }

程序清单4.22

 1 #include<iostream>
 2 #include<cstring>
 3 using namespace std;
 4 
 5 char * getname() {
 6     char temp[80];
 7     cout << "Enter last name:";
 8     cin>>temp;
 9     char *pn = new char[strlen(temp) + 1];//长度+1：包括一个空字符
10     strcpy(pn, temp);
11     return pn;
12 }
13 
14 void main(){
15     char * name;
16     name = getname();
17     cout << name << " at " << (int *) name << endl;
18     delete[] name;
19 
20     name = getname();
21     cout << name << " at " << (int *) name << endl;
22     delete[] name;
23 
24     system("pause");
25 }

两次地址可能相同，也可能不同。

程序清单4.23（类型组合）

 1 #include<iostream>
 2 #include<cstring>
 3 using namespace std;
 4 
 5 struct Student {
 6     int age;
 7 };
 8 
 9 void main(){
10     Student s1, s2, s3;
11     s1.age = 19;
12     Student *p = &s2;
13     p->age = 20;
14     Student ss[3];
15     ss[0].age = 22;
16 
17     cout << "ss[0].age=" << ss->age << endl;
18 
19     const Student * arp[3] = { &s1,&s2,&s3 };//指针数组：由指针组成的数组
20     cout << "s1.age="<<arp[0]->age<< endl;
21 
22     const Student **ppa = arp;//arp是数组名称，即第一个元素的地址，而第一个元素为指针，所以ppa是二级指针
23     auto ppb = arp;//自动推断类型
24     cout << "s1.age=" << (*ppa)->age << endl;
25     cout << "s2.age=" << (*(ppa+1))->age<< endl; //ppa + 1指向arp[1]，即&s2
26     //cout << "s2.age=" << (*ppa + 1)->age << endl;        错误！
27 
28     system("pause");
29 }

程序清单4.24(数组的替代品，array，vector)

 1 #include<iostream>
 2 #include<vector>
 3 #include<array>
 4 using namespace std;
 5 
 6 void main() {
 7     double a[4] = { 1.2,2.4,3.6,4.8 };
 8     vector<double> b(4);
 9     b[0] = 1.0 / 3.0;
10     b[1] = 1.0 / 5.0;
11     b[2] = 1.0 / 7.0;
12     b[3] = 1.0 / 9.0;
13     array<double, 4> c = { 3.14,2.72,1.62,1.41 };
14     array<double, 4> d;
15     d = c;
16 
17     cout << "a[2]:" << a[2] << " at " << &a[2]<<  endl;//&a[2]=a + 2
18     cout << "b[2]:" << b[2] << " at " << &b[2] << endl;
19     cout << "c[2]:" << c[2] << " at " << &c[2] << endl;
20     cout << "d[2]:" << d[2] << " at " << &d[2] << endl<<endl;
21 
22     a[-2] = 20.2;//a[-2]=*(a-2)
23     cout << "a[2]:" << a[-2]<< " at " << &a[-2]<< endl;
24     cout << "c[2]:" << c[2] << " at " << &c[2] << endl;
25     cout << "d[2]:" << d[2] << " at " << &d[2] << endl;
26 
27     system("pause");
28 }

注意：无论是数组，vector还是array对象，都可以使用数组表示法来访问各个元素。其次，从地址可知，array和数组都是存储在栈中，而vector存储在自由存储区或堆中。第三，可以将array对象赋给另一个array对象；而对于数组，必须逐元素复制。

索引-2转换为：a[-2]=*(a-2)