c++ - why does my cin loop never end? -

in following code, if user inputs not int, program goes infinite loop. why happen, , should fix it?

#include <iostream> #include <string> using namespace std;   int main() {     int i;     char str[100];     while (!(cin >> i))     {         gets(str);         cout << "failure read!" << endl;     }      cout << "successful read!" << endl;     return 0; } 

clear error state:

int main() {     int i;     char str[100];     while (!(cin >> i))     {         cin.clear();         cin.getline(str,100);         cout << "failure read!" << endl;     }      cout << "successful read!" << endl;     return 0; }