[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

 #include<iostream>
 using namespace std;

 void main(){
     int yams[];
     yams[]=;
     yams[]=;
     yams[]=;
     int yams_cost[]={,,}; 

     cout<<"Total yams="<<yams[]+yams[]+yams[]<<endl;
     cout<<"The package with "<<yams[]<<" yams costs "<<yams_cost[]<<" cents per yam"<<endl;
     cout<<"Total costs="<<yams[]*yams_cost[]+yams[]*yams_cost[]+yams[]*yams_cost[]<<" cents"<<endl;

     cout<<"Size of yams array="<<sizeof(yams)<<" bytes"<<endl;
     cout<<"Size of yams[0]="<<sizeof(yams[])<<" bytes"<<endl;

     system("pause");
 }

程序清单4.2

 #include<iostream>
 #include<cstring>//strlen(),c语言版为string.h
 using namespace std;

 void main(){
     const int size=;
     char name1[size];//char占一个字节
     char name2[size]="C++owboy";

     cout<<"I am "<<name2<<".What's your name?"<<endl;
     cin>>name1;
     cout<<"Well,"<<name1<<",your name has "<<strlen(name1)<<" letters and is stored in an array of "<<sizeof(name1)<<" bytes"<<endl;
     cout<<"Your initial is "<<name1[]<<endl;
     name2[]='\0';
     cout<<"Here are the first 3 characters of my name:"<<name2<<endl;
     system("pause");
 }

程序清单4.3

 #include<iostream>
 using namespace std;

 void main(){
     const int size=;
     char name[size];
     char dessert[size];

     cout<<"What's your name?"<<endl;
     cin>>name;
     cout<<"What's your favorate dessert?"<<endl;
     cin>>dessert;
     cout<<"I have some delicious "<<dessert<<" for you."<<endl;
     system("pause");
 }

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

 #include<iostream>
 using namespace std;

 void main(){
     const int size=;
     char name[size];
     char dessert[size];

     cout<<"What's your name?"<<endl;
     cin.getline(name,size);
     cout<<"What's your favorate dessert?"<<endl;
     cin.getline(dessert,size);
     cout<<"I have some delicious "<<dessert<<" for you."<<endl;
     system("pause");
 }

程序清单4.6

 #include<iostream>
 using namespace std;

 void main(){
     cout<<"你房子哪一年修的?"<<endl;
     int year;
     cin>>year;
     cout<<"房子的地址?"<<endl;
     char address[];
     cin.getline(address,);
     cout<<"Year built:"<<year<<endl<<"Address:"<<address<<endl<<"Done!";
     system("pause");
 }

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)

 #include<iostream>
 #include<string>
 using namespace std;

 void main(){
     char ch1[];
     char ch2[]="jaguar";
     string str1;
     string str2="panther";

     cout<<"enter a kind of feline:";
     cin>>ch1;
     cout<<"enter another kind of feline:";
     cin>>str1;
     cout<<"Here are some felines:\n"<<ch1<<" "<<ch2<<" "<<str1<<" "<<str2<<endl;
     cout<<"The third letter in "<<ch2<<" is "<<ch2[]<<endl;
     cout<<"The third letter in "<<str2<<" is "<<str2[]<<endl;
     system("pause");
 }

程序清单4.8(string赋值、拼接和附加)

 #include<iostream>
 #include<string>
 using namespace std;

 void main(){
     string str="penguin";
     string str2,str3,str4;

     str2=str;
     cout<<"str2="<<str2<<endl;
     str3="buzzard";
     cout<<"str3="<<str3<<endl;
     str4=str+str3;
     cout<<"str4="<<str4<<endl;
     str+=str3;
     cout<<"str="<<str<<endl;
     str2+=" is cute!";
     cout<<"str2="<<str2<<endl;
     system("pause");
 }

程序清单4.9（cstring）

 #include<iostream>
 #include<string>
 #include<cstring>//strcpy,strcat,strlen
 using namespace std;

 void main(){
     char ch1[];
     char ch2[]="jaguar";
     string str1;
     string str2="panther";

     str1=str2;
     strcpy(ch1,ch2);

     str1+=" paste";
     strcat(ch1," juice");

     int len1=str1.size();
     int len2=strlen(ch1);

     cout<<"the string "<<str1<<" contains "<<len1<<"  characters"<<endl;
     cout<<"the string "<<ch1<<" contains "<<len2<<"  characters"<<endl;

     system("pause");
 }

程序清单4.10

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

 void main(){
     char ch[];
     string str;

     cout<<"Length of string in ch before input:"<<strlen(ch)<<endl;
     cout<<"Length of string in str before input:"<<str.size()<<endl;
     cout<<"Enter a line of text:"<<endl;
     cin.getline(ch,);
     cout<<"You entered:"<<ch<<endl;
     cout<<"Enter another line of text:"<<endl;
     getline(cin,str);
     cout<<"You entered:"<<str<<endl;
     cout<<"Length of string in ch after input:"<<strlen(ch)<<endl;
     cout<<"Length of string in str after input:"<<str.size()<<endl;

     system("pause");
 }

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)

 #include<iostream>
 using namespace std;

 struct  table{
     char name[];
     float volumn;
     double price;
 };

 void main(){
     table guest={"GG",1.88,29.99};
     table pal={"AA",3.12,32.99};
     cout<<"Expand your guest list with "<<guest.name<<" and "<<pal.name<<endl;
     cout<<"You can have both for  $"<<guest.price+pal.price<<endl;

     cout<<"------------------------------"<<endl;

     table choice=guest;
     cout<<"choice:"<<choice.name<<" for $"<<choice.price<<endl;

     system("pause");
 }

程序清单4.13

 #include<iostream>
 using namespace std;

 struct  table{
     char name[];
     float volumn;
     double price;
 };

 void main(){
     table guest[]={
         {"GG",1.88,29.99},
         {"AA",3.12,32.99}
     };
     cout<<"The guests "<<guest[].name<<" and "<<guest[].name<<endl<<"have a combined volumn of "<<guest[].volumn+guest[].volumn<<" cubic feet"<<endl;

     system("pause");
 }

程序清单4.17(指针：new)

 #include<iostream>
 using namespace std;

 void main(){
     int nights=;
     int *pt = new int;
     *pt = ;
     double *pd = new double;
     *pd = 100000000000.1;

     cout << "nights value=" << nights << ":location " << &nights << endl;
     cout << "int value=" <<*pt<< ":location " <<pt<< endl;
     cout << "double value=" << *pd << ":location " << pd << endl;
     cout << "location of pointer pd:" << &pd<< endl;

     cout << "size of pt=" <<sizeof(pt)<< endl;
     cout << "size of *pt=" << sizeof(*pt) << endl;
     cout << "size of pd=" << sizeof(pd) << endl;
     cout << "size of *pd=" << sizeof(*pd) << endl;

     system("pause");
 }

程序清单4.18(new完之后要delete)

 #include<iostream>
 using namespace std;

 void main() {
     double *p = new double[];//使用new创建动态数组
     p[] = 0.2;
     p[] = 0.5;
     p[] = 0.8;
     cout << "p[1]=" << p[] << endl;
     p++;
     cout << "Now p[0]=" << p[] << endl;
     cout << "p[1]=" << p[] << endl;
     p--;
     cout << "And now p[0]=" << p[] << endl;
     delete[] p;//回归初始位置释放内存
     getchar();
 }

程序清单4.19

 #include<iostream>
 using namespace std;

 void main() {
     double wages[] = { 10000.0,20000.0, 30000.0 };
     short stacks[] = {  ,  ,  };
     double * pw = wages;
     short * ps = &stacks[];

     cout << "pw=" << pw <<",*pw="<<*pw<< endl;
     pw++;
     cout << "Now,pw=" << pw << ",*pw=" << *pw << endl;
     cout << "ps=" << ps << ",*ps=" << *ps << endl;
     ps++;
     cout << "Now,ps=" << ps << ",*ps=" << *ps << endl;

     cout << "stacks[0]=" << stacks[] << ",stacks[1]=" << stacks[] << endl;
     cout << "*stacks=" << *stacks<< ",*(stacks+1)=" << *(stacks + ) << endl;
     cout << "sizeof(wages)=" << sizeof(wages)<< endl;
     cout << "sizeof(pw)=" << sizeof(pw) << endl;

     getchar();
 }

程序清单4.20

 #define _CRT_SECURE_NO_WARNINGS
 #include<iostream>
 #include<cstring>
 using namespace std;

 void main() {
     char animal[] = "bear";
     const char * bird = "wren";
     char * ps;

     cout << animal <<" and "<< bird << endl;
     cout << "Enter a kind of animal:";
     cin >> animal;
     ps = animal;
     cout << "ps="<<ps<< endl;
     cout << "Before using strcpy()： \n ";
     cout << animal << " at " << (int *)animal << endl;
     cout << ps << " at " << (int *)ps << endl;

     ps = new char[strlen(animal) + ];
     strcpy(ps, animal);
     cout << "After using strcpy()： \n ";
     cout << animal << " at " << (int *)animal << endl;
     cout << ps << " at " << (int *)ps << endl;
     delete[] ps;

     system("pause");
 }

程序清单4.21

 #include<iostream>
 using namespace std;

 struct inflatable {
     char name[];
     float volumn;
     double price;
 };

 void main() {
     inflatable *ps = new inflatable;

     cout <<"Enter name of inflatable item:";
     cin.get(ps->name,);
     cout << "Enter volumn in cubic feet:";
     cin>>(*ps).volumn;
     cout << "Enter price:$";
     cin >>ps->price;

     cout << "Name:" << (*ps).name<< endl;
     cout << "Volumn:" <<ps->volumn<< endl;
     cout << "Price:" <<ps->price<< endl;
     delete ps;

     system("pause");
 }

程序清单4.22

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

 char * getname() {
     char temp[];
     cout << "Enter last name:";
     cin>>temp;
     char *pn = new char[strlen(temp) + ];//长度+1：包括一个空字符
     strcpy(pn, temp);
     return pn;
 }

 void main(){
     char * name;
     name = getname();
     cout << name << " at " << (int *) name << endl;
     delete[] name;

     name = getname();
     cout << name << " at " << (int *) name << endl;
     delete[] name;

     system("pause");
 }

两次地址可能相同，也可能不同。

程序清单4.23（类型组合）

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

 struct Student {
     int age;
 };

 void main(){
     Student s1, s2, s3;
     s1.age = ;
     Student *p = &s2;
     p->age = ;
     Student ss[];
     ss[].age = ;

     cout << "ss[0].age=" << ss->age << endl;

     const Student * arp[] = { &s1,&s2,&s3 };//指针数组：由指针组成的数组
     cout << "s1.age="<<arp[]->age<< endl;

     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
     auto ppb = arp;//自动推断类型
     cout << "s1.age=" << (*ppa)->age << endl;
     cout << "s2.age=" << (*(ppa+))->age<< endl; //ppa + 1指向arp[1]，即&s2
     //cout << "s2.age=" << (*ppa + 1)->age << endl;        错误！

     system("pause");
 }

程序清单4.24(数组的替代品，array，vector)

 #include<iostream>
 #include<vector>
 #include<array>
 using namespace std;

 void main() {
     double a[] = { 1.2,2.4,3.6,4.8 };
     vector<double> b();
     b[] = 1.0 / 3.0;
     b[] = 1.0 / 5.0;
     b[] = 1.0 / 7.0;
     b[] = 1.0 / 9.0;
     array<double, > c = { 3.14,2.72,1.62,1.41 };
     array<double, > d;
     d = c;

     cout << "a[2]:" << a[] << " at " << &a[]<<  endl;//&a[2]=a + 2
     cout << "b[2]:" << b[] << " at " << &b[] << endl;
     cout << "c[2]:" << c[] << " at " << &c[] << endl;
     cout << "d[2]:" << d[] << " at " << &d[] << endl<<endl;

     a[-] = 20.2;//a[-2]=*(a-2)
     cout << "a[2]:" << a[-]<< " at " << &a[-]<< endl;
     cout << "c[2]:" << c[] << " at " << &c[] << endl;
     cout << "d[2]:" << d[] << " at " << &d[] << endl;

     system("pause");
 }

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)