深度学习C++复合类型

引言

下面我们来看下C++中复合类型的数据使用案例。

getline()

#include <iostream>

int main() {
    using namespace std;
    const int ArSize = 20;
    char name[ArSize];
    char dessert[ArSize];
    cout << "Enter your name:\n";
    cin.getline(name, ArSize);
    cout << "Enter your favorite dessert:\n";
    cin.getline(dessert, ArSize);
    cout << "I have some delicious " << dessert;
    cout << " for you, " << name << ".\n";
    return 0;
}

输出：

D:\CODE\cpp\cmake-build-debug\cpp.exe
Enter your name:
zhangpan
Enter your favorite dessert:
打游戏，看书
I have some delicious 打游戏，看书 for you, zhangpan.

Process finished with exit code 0

string

#include <iostream>
#include <string>
#include <cstring>

int main() {
    using namespace std;
    string str1;
    string str2 = "alspd";
    char charr1[20] = "zhangpan";
    char charr2[20];
    strcpy(charr2, "hello");
    cout << "charr2:" << charr2 << endl;
    cout << "str2.size(): " << str2.size() << endl;

    cout << str2 << endl;
}

输出：

D:\CODE\cpp\cmake-build-debug\cpp.exe
charr2:hello
str2.size(): 5
alspd

Process finished with exit code 0

结构体

C++允许再声明结构体变量时省略关键字struct,C++提倡使用外部结构变量

#include <iostream>

struct inflatable
{
    char name[20];
    float volume;
    double price;
};

int main() {
    using namespace std;
    inflatable guest = {
            "zhangpan",
            1.88,
            29.99
    };
    inflatable pal = {
            "alspd",
            3.12,
            32.99
    };

    cout << "guest.name:" << guest.name << endl;
    cout << "pal.name:" << pal.name << endl;
    cout << "pal.price:" << pal.price << endl;
    
    //省略=
    inflatable duck {"zhangsan", 2.3, 3.3};
    inflatable mayor {};//默认哥哥成员设置为零
}

输出：

D:\CODE\cpp\cmake-build-debug\cpp.exe
guest.name:zhangpan
pal.name:alspd
pal.price:32.99

Process finished with exit code 0

枚举

创建符号常量得方式，可以代替const

enum spectrum{red, orange, yellow, green, blue, violet, indigo, ultraviolet};

枚举量得值从0开始

指针

指针是一个变量，存储得是值的地址，而不是值本身。只需对变量应用地址运算符（&）
*运算符为解引用运算符

#include <iostream>

int main() {
    using namespace std;
    int updates = 6;
    int * p_updates;
    p_updates = &updates;

    //express values two ways
    cout << updates << endl;
    cout << *p_updates << endl;

    //express address two ways
    cout << &updates << endl;
    cout << p_updates << endl;

    // use pointer to change value
    *p_updates = *p_updates + 1;
    cout << updates << endl;
    return 0;
}

输出：

D:\CODE\cpp\cmake-build-debug\cpp.exe
6
6
0x61fe14
0x61fe14
7

Process finished with exit code 0

指针危险性：一定要在对指针应用解引用运算符（*）之前，将指针初始化为一个确定的地址。

指针真正的用武之地，在于运行阶段分配未命名的内存以存储值，下面来看看

指针 new delete

只能用delete来释放使用new分配的内存。

#include <iostream>

int main() {
    using namespace std;
    int nights = 1001;
    int * pt = new int;
    * pt = 1001;
    cout << nights << endl;
    cout << pt << endl;
    cout << *pt << endl;
    delete pt;
    double * pd = new double;
    *pd = 1000001.0;
    cout << *pd << endl;
    *pd = 2000002.0;
    cout << *pd << endl;
    delete pd;

}

输出：

D:\CODE\cpp\cmake-build-debug\cpp.exe
1001
0x21730
1001
1e+06
2e+06

Process finished with exit code 0

使用new来创建动态数组

格式：
int * pt = new int [10]
delete [] pt

#include <iostream>

int main() {
    using namespace std;
    double * p3 = new double [3];
    p3[0] = 0.2;
    p3[1] = 0.5;
    p3[2] = 0.8;
    cout << p3[1] << endl;
    p3 = p3 + 1;//increment the pointer
    cout << p3[1] << endl;
    cout << p3[0] << endl;
}

输出：

D:\CODE\cpp\cmake-build-debug\cpp.exe
0.5
0.8
0.5

Process finished with exit code 0

结语

指针这块非常重要，后面会专门讲。