Ｃ++笔记之零碎点

1，测试cin.ignore（）的作用，用于去除缓冲区的残留数据 

#include <iostream>

int main()
{
    char buff[20];
    char buff1[20];

    std::cin >> buff1;
    std::cin.ignore(7, '
');       // 通常把获取前n个字符写的很大，去掉前一次输入的‘
’
    std::cin.getline(buff, 10);     // 只能获取９个，存最末尾储''

    std::cout << buff << std::endl;

    return 0;
}

2.整形的占用位数

#include <iostream>
#include <climits>

int main()
{
    using namespace std;

    int n_int = INT_MAX;
    short n_short = SHRT_MAX;
    long n_long = LONG_MAX;
    long long n_llong = LLONG_MAX;

    cout << "int      : " << sizeof n_int << "bytes." << endl;
    cout << "short    : " << sizeof n_short << "bytes." << endl;
    cout << "long     : " << sizeof n_long << "bytes." << endl;
    cout << "long long: " << sizeof n_llong << "bytes." << endl;
    cout << endl;

    cout << "Maximum values:" << endl;
    cout << "int      : " << n_int << endl;
    cout << "short    : " << n_short << endl;
    cout << "long     : " << n_long << endl;
    cout << "long long: " << n_llong << endl;
    
}

运行结果： 

int      : 4bytes.
short    : 2bytes.
long     : 8bytes.
long long: 8bytes.

Maximum values:
int      : 2147483647
short    : 32767
long     : 9223372036854775807
long long: 9223372036854775807

3，整形溢出 

4，cin的相关方法 - ignore，get，getline，peek，gcount，read 

#include <iostream>
#include <climits>
using namespace std;
int main()
{
    const int SIZE = 50;
    char buff[SIZE];

    cout << "请输入一段文本：";
    cin.read(buff, 10);         //读取输入，阻塞计数，不忽略回车

    cout << "输入的文本字符数为：" << cin.gcount() << endl;  //统计

    cout << "输入的文本信息是：";
    cout.write(buff, 19);       //读取缓冲区数据，打印
    cout << endl;

    return 0;

}

运行结果： 

请输入一段文本：yfu
67t
87y
输入的文本字符数为：10
输入的文本信息是：yfu
67t
8

5，文件复制

此处换行符会被过滤掉，所以逐行读取，手动添加ENDL。

#include <iostream>
#include <climits>
#include <fstream>

using namespace std;
int main()
{
    ifstream in; //文件输入流类对象
    in.open("../test.txt", ios::binary); //用两种方法来打开文件
    ofstream out("../test1.txt", ios::binary | ios::app); //文件输出流类对象

    if(!in){
        cerr << "打开文件失败" << endl;
        return 0;
    }

//    char x;
//    while( in >> x){
//        if(x != '
'){
//            cout << x;
//            out << x;
//        }
//        else{
//            cout << "遇到换行";
//            out << "-------********
";
//        }

    in.seekg(ios::beg); //指针指向文件头

    for(string s; getline(in, s);){
        cout << s << endl;
        out << s << endl;
    }

    cout << endl;

    in.close();
    out.close();

    return 0;
}

6，输入输出，切换循环

#include <iostream>

int main()
{
    char answer;

    std::cout << "请问你毕业了吗？[Y/N]" << std::endl;
    std::cin >> answer;

    switch(answer){
        case 'Y':
        case 'y':
            std::cout << "你毕业了！" << std::endl;
            break;

        case 'N':
        case 'n':
            std::cout << "你怎么还没有毕业！" << std::endl;
            break;

        default:
            std::cout << "输入不符合要求！！！" << std::endl;
            break;
    }

    std::cin.ignore(100, '
');

    std::cout << "输入任何字符结束" << std::endl;
    std::cin.get();

}

如图7所示，温度转换（我写的第一个C ++程序）

#include <iostream>

int main()
{
    // 输入选择，确定公式
    char answer;
    std::cout << "请问待转换的温度单位序号：
"
              << "1. 华氏度(℉) 
"
              << "2. 摄氏度(℃) " << std::endl;
    std::cin >> answer;

    // 输入温度值
    float temperature;
    std::cout << "请输入当前温度：" << std::endl;
    std::cin.ignore(100, '
');
    std::cin  >> temperature;

    //　进行判断，输出结果
    float f2c(float num);
    float c2f(float num);
    float result = -1000;

    switch(answer){
        case '1':
            result = f2c(temperature);
            break;
        case '2':
            result = c2f(temperature);
            break;
        default:
                        std::cout << "输入不符合要求！！！" << std::endl;
            break;
    }

    if(result != -1000){
        std::cout << result << std::endl;
    }
    else{
        std::cout << "输入错误" << std::endl;
    }

}

float f2c(float num){
    // 摄氏度 = 【(华氏度 - 32) ÷ 1.8】℃
    float result;

    result = (num-32) ;
    result /= 1.8;

    return result;
}

float c2f(float num){
    // 华氏度 = (32 + 摄氏度 × 1.8)℉
    float result;

    num *= 1.8 ;
    result = num + 32;

    return result;
}

手痒写一个Python的版本：

temper = input('请输入温度，形如【23.2 C】或者【23.2 F】')
temp_value, temp_type = temper.split(' ')

temp_value = float(temp_value)
temp_type = temp_type.upper()

print(temp_type, temp_value)
if (temp_type == 'C') :
    result = str(round(temp_value*1.8 + 32, 2)) + '℉'
elif(temp_type == 'F') :
    result = str(round((temp_value-32)/1.8, 2)) + '℃'
else:
    result = None
    print('输入有误')

print(result)

8.地址运算符和间接值运算符的使用

运行结果如下： 

Values: updates = 6, *p_updates = 6
Addresses: &updates = 0x7ffd2f82ce0c, &p_updates = 0x7ffd2f82ce0c

可见，对变量名对应地址取间接运算符，相当与获得变量名对应值。

9.数组的指针地址

#include<iostream>
#include<string>
#include <limits>

int main()
{
    const unsigned short ITEMS = 5;

    int intArray[ITEMS] = {1, 2, 3, 4, 5};
    char charArray[ITEMS] = {'f', 'I', 'j', 'K', ';'};

    int *intPtr = intArray;
    char *charPtr = charArray;
    
    //显示整形数组的内存地址
    std::cout << "整型数组输出：" << '
';
    for (int i = 0; i < ITEMS; i++) {
        std::cout << *intPtr << " at " << reinterpret_cast<unsigned long>(intPtr) << std::endl;
        intPtr++;
    }
    
    //显示字节型数组的内存地址和指针对打印的影响
    std::cout << "字符型数组输出：" << '
';
    for (int i = 0; i < ITEMS; i++) {
        std::cout << *charPtr << " at " << reinterpret_cast<unsigned long>(charPtr) << " - " << charPtr << std::endl;
        charPtr++;
    }
    
    //测试运算
    int *temp = intArray;
    std::cout << *temp+1<< std::endl;
    std::cout << *(temp+1) << std::endl;
    return 0;
};

9.字符串指针，动态创建

#include <iostream>
#include <string>

using namespace std;

int main()
{
    const int num = 5;
    
    string temp;
    auto *plist  = new string [num];

    for (int i = 0; i<num; i++) {
        cout << "请输入第" << i+1 << "个字符" << endl;
        cin >> temp;

        plist[i] = temp;
    }

    cout << plist->length() << endl; //4个字节，64位系统

    for (int i = 0; i<num; i++) {
        cout << plist << " --- " <<  plist[0] << endl; //不是plist[i]
        plist ++;   //指针加法，指向下一个字符
    }
    
}

10.输出阶乘

#include <iostream>
#include <string>

using namespace std;

struct student{
    char age[20];
    char gender[20];
    string name;
};

const int Arsize = 16;

int main()
{
    long long factor[Arsize];
    factor[0] = factor[1] = 1LL;

    for (int i = 2; i<Arsize; i++) {
        factor[i] = factor[i-1] *i;
    }

    for (long long i : factor) {
        cout << i << "! = " << i << endl;
        
    }
}

 11. 枚举和switch的组合使用

#include <iostream>
#include <string>
#include <vector>

using namespace std;

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

int main() {
    cout << "请输入你的选择(0-6): 
";

    int code;

    while (cin >> code && code >= 0 && code <= 6) {
        switch (code) {
            case red:
                cout << 0 << endl;
                break;
            case orange:
                cout << 1 << endl;
                break;
            case yellow:
                cout << 2 << endl;
                break;
            case green:
                cout << 3 << endl;
                break;
            case blue:
                cout << 4 << endl;
                break;
            case violet:
                cout << 5 << endl;
                break;
            case indigo:
                cout << 6 << endl;
                break;
            default:
                cout << "输入有误，退出" << endl;
                break;
        }
        cout << "跳出选择
";
    }
    cout << "跳出循环
";
    return 0;
}

12. 带回车的字符串输入

#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main()
{
    string input{};
    int count{};

    cout << "请输入你需要的字符,用*结尾" << endl;
    getline(cin, input, '*');
    count = static_cast<int>(input.length());

    cout << "字符个数为：" << input << endl;

}