Several functions that need to be clarified urgently, urgently~~~~!!!

weiba0110

The specific usage of in, cin, sin, getline() and what operator is encountered to stop input
If there is a file to enter:
aaa.txt:
5
1 2 4 5 2 3 7 8
9 8 9
4 0 9 8 2
What is the difference between input using these 4 methods, and what is the result?
What does ignore() mean, and how to use it? Hope you all give me some pointers, thank you!

firegun

in,sin//No such thing, it should be in or sin in istream in("a.txt");
Cin//The global object of istream stored in iostream, usage:
int i;
cin>>i;
string t;
cin>>t;

getline usage
    std::string s;
    while (getline(std::cin,s)) {//End with '\n'
        ...
    }
    while (getline(std:: cin, s,':')) {//End with':'
        ...
    }

In addition, istream also has a getline member function, usage:
getline(s, num) can read at most num -1 characters, ending with '\n', including '\n'
getline(s, num, t) ends with t, others are the same as above

ignore():
istream&istream::ignore ()//Skip a character

istream&istream::ignore (streamsize count)//Skip count characters

istream&istream::ignore (streamsize count, int delim)//Skip count characters or encounter delim

weiba0110

The default of ignore() is to skip carriage returns or space characters?