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这个问题源自于之前调试AVL树时，要输入两次值，我在第一次cin时，用CTRL+Z结束输入，之后的cin 程序执行直接就跳过了，不能输入了；；；

解决方法：在第一次输入后的程序加上以下两句时就可以了；

cin.clear();//cin.sync();

分析：CTRL + Z后；eof、fail 位都会true；clear()之后good位位true；

io标准库条件状态成员；

代码测试：

#include using namespace std;int main(){    int num;    cout << "first num :" << endl;    while(cin >> num) { }    cout << "first num  is:" << num << endl;    cout << "goodbit:" << cin.good() << endl;    cout << "eofbit :" << cin.eof() << endl;    cout << "failbit:" << cin.fail() << endl;    cout << "badbit :" << cin.bad() << endl;        cin.clear();    cout << "after clear()" << endl;    cout << "goodbit:" << cin.good() << endl;    cout << "eofbit :" << cin.eof() << endl;    cout << "failbit:" << cin.fail() << endl;    cout << "badbit :" << cin.bad() << endl;    int tmp;    cin >> tmp;    cout << "second num: " << tmp << endl;    system("pause");    return 0;}/*没有cin.clear()的输出：first num :10^Zfirst num  is:10goodbit:0eofbit :1failbit:1badbit :0second num: 6422400请按任意键继续. . .*//*first num :10^Zfirst num  is:10goodbit:0eofbit :1failbit:1badbit :0after clear()goodbit:1eofbit :0failbit:0badbit :011second num: 11请按任意键继续. . .*/