int N;
    char c;
    int num=0;
    string s;
     cin>>N>>c;

     getline(cin,s,‘\n‘);
     for(int i=0; s[i]!=‘\0‘;i++)
     {
         num++;
     }
     cout<<num<<endl;

這時cin（輸入流）的狀態被標誌為遇到文件結尾，如果不調用in.clear()或其他可以清除流的狀態的函數來將清除cin的狀態，則cin被標誌為遇到文件結尾的狀態一起保持。到第二個 getline(cin, line)再次引用cin，則此時的cin的狀態為遇到文件結束標誌，無法輸入，因此num始終為0；

一.調用clear()來清除cin的狀態

二.cin.flush();

三.cin.ignore();

總有一款適合你……嘗試了好多次，終於可以了！

string word;
// read until end-of-file, writing each word to a new line
cout<<"\nNow you can input as many words as you can. If you want to terminate, you may press Ctrl+z:\n";
while (cin >> word)
cout << word << endl;

cin.clear();//調用clear()來清除cin的狀態

string line;
// read line at time until end-of-file
cout<<"\nNow you can input as many lines of words as you wish. To terminate, please press Ctrl+z:\n";
while (getline(cin, line))
cout << line << endl;
cin.clear();

keep_window_open();

關於cin,getline一起出現無法正常輸入的問題