for (int i = 0; i < 5; i++)
    {
        cout << "abc"<< endl;
    }

    for (int i = 5; i; i--)
    {
        cout << "abc" << endl;
    }

    int a = 0;
    while (a<10)
    {
        a++;
        cout << a << endl;
    }

    int a = 0;
    do
    {
        a++;
        cout << a << endl;
    } while (a<5);

    int a[] = { 3,6,8,7 };
    for (int i:a)
    {
        cout << i << endl;
    }

    int a[] = { 3,6,8,7 };
    for (int &i:a)
    {
        cout << i << endl;
    }

    for (int i: { 3,6,8,7 })
    {
        cout << i << endl;
    }

    char ch;
    int count = 0;
    cout << "输入字符，按#结束";
    cin >> ch;
    while (ch != ‘#‘) {
        cout << ch;
        ++count;
        cin >> ch;
    }
    cout << count << endl;

    char ch;
    int count = 0;
    cout << "输入字符，按#结束";
    cin.get(ch);
    while (ch != ‘#‘) {
        cout << ch;
        ++count;
        cin.get(ch);
    }
    cout << count << endl;

    int arr[3][3] = { {1,2,3},{4,5,6},{7,8,9} };
    int c = 0;
    for (int i=0; i<3;i++)
    {
        for (int j = 0; j < 3;j++) {
            c = arr[i][j];
            cout << c << endl;
        }
    }

    if () {
        //
    }
    else if ()
    {
        //
    }
    else
    {
        //
    }

if (a> 0 && a<5) {
    //
}
if (a< 0 || a>5) {
    //
}

#include<cctype>
isalnum() //判断是否数字或字母
isalpha() //是否字母
iscntrl() //是否控制字符
isdigit() //是否0-9
isgraph() //是否除空格之外的打印字符
islower() //是否小写字母
isprint() //是否打印字符
ispunct() //是否标点符号
isspace() //是否标准空白字符（空格，进纸，换行，回车，制表）
isupper() //是否大写字母
isxdigit() //是否十六进制
tolower() //如果是大写，返回小写
toupper() //如果是小写，返回大写

    char ch = 1 > 3 ? ‘a‘ : ‘b‘;
    cout << ch;

    char ch = ‘c‘;
    switch (ch)
    {
    case ‘a‘:
    case ‘A‘:
        cout << ch;
        break;
    default:
        cout << "off";
    }