c++ - Why does this code end up in an infinite loop, reading from std::cin -

hi try create input function function through vector.

however, don't know why input become infinite loop?

do {                 cout << "please enter next number: ";     cin >> num;     number.push_back(num);     cout << "do want end? enter 0 continue.";     dec = null;     cin >> dec; } while(dec == 0); 

"i don't know why input become infinite loop."

the reason can imagine is, incorrect input sets cin fail state. in case (e.g. invalid number entered, or enter pressed) cin set fail state , value in dec won't change evermore. once cin in fail state subsequent input operations fail respectively, , subject input won't changed.

to proof against such behavior, have clear() std::istream's state, , read safe point, before proceeding (see also: how test whether stringstream operator>> has parsed bad type , skip it):

do {     cout << "please enter next number: ";     if(cin >> num) {         number.push_back(num);     }     else {        cerr << "invalid input, enter number please." << std::endl;        std::string dummy;          cin.clear();        cin >> dummy;     }     cout << "do want end? enter 0 continue.";     dec = -1;     if(!(cin >> dec)) {        std::string dummy;          cin.clear();        cin >> dummy;        break; // escape loop if other 0               // typed in     } } while(dec == 0); 

here 3 working demos different inputs end loop:

1st input:

1 0 2 0 3 0 4 

enter

2nd input:

1 0 2 0 3 0 4 xyz 

3rd input

1 0 2 0 3 0 4 42 

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the loop finite, , output of above

1234 

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_{should note have changed bool dec; int dec;, that's minor point.}