请问（A）处的cin代表什么意思啊
int main()
{
    using namespace std;
    char input[Arsize];
    char next;
    cout<<"enter a line: \n";
    cin.get(input,Arsize);
    while(cin)                                         （A）
    {
        cin.get(next);
        while(next!='\n')
            cin.get(next);
        strcount(input);
        cout<<"enter next line(empty line to quit): \n";
        cin.get(input,Arsize);
    }
    cout<<"Bye\n";
    return 0;
}

1到3处的代码在程序中是什么意思啊，谁能帮我解释下
int main()
{
    using namespace std;
    char input[Arsize];
    char next;
    cout<<"enter a line: \n";
    cin.get(input,Arsize);
    while(cin)                                       
    {
        cin.get(next);                              1
        while(next!='\n')                           2
            cin.get(next);                          3
        strcount(input);
        cout<<"enter next line(empty line to quit): \n";
        cin.get(input,Arsize);
    }
    cout<<"Bye\n";
    return 0;
}