c++ - Why does this do while loop repeat infinitely? -

i want prompt user input integer, if user enters non-integer, program should keep demanding integer until user complies.

int getinteger(){     int input;      do{         std::cout << "enter integer: ";         std::cin >> input;     } while(!(std::cin));       return input; } 

if user enters integer, function returns it.

but if user enters "hello," function goes on infinite, cout-ing "enter integer: ".

how fix this?

!(std::cin) 

will evaluate true if std::cin in bad state, e.g. after input operation failed. then, subsequent input operations fail , not change cin's error state, infinite loop.

to behavior want, may use like

while (!(std::cin >> input)) {     std::cout << "try again\n";     // clear away error state     std::cin.clear();             // ignore ever garbage still in stream     std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');  } 

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in real world, may want handle (generally not recoverable) failures eof (someone sent end of file character) , bad (cin broken, should not happen) different fail happens after invalid input. is, example, shown on this reference page ignore. however, should not bite in toy programs yours seems be.