c++ - cin fails to stop while loop -

I was wondering if you can tell me why this loop can not find if I say 'r' value ' Value of

  Double Values ​​std :: cout & lt; & Lt; "Please enter a real number:"; Std :: cin & gt; & Gt; value; While (! Isdigit (value)) {std :: cout & lt; & Lt; "Sorry, but only numbers are valid. \ NPlease enter a real number:"; Std :: cin & gt; & Gt; value; }  

Thanks a lot.

You should not be using isdigit () because it To test whether a single char type is an ASCII digit.

If you are expecting a user to enter a real number (and not a string), you can use cin.fail () to use your code. should do. If cin is expecting a double , then reads a string, then cin.fail () return true .

Another (cleaner) option is to test the status of cin , as @bangfs reported:

  While ( 

( gt; value)) {// bad value was entered!