As a good programmer, you test your app in all possible conditions. Dart defines a number of errors for those things that you should remedy in your code, such as CastError when a cast fails, or NoSuchMethodError when the class of the object on which the method is called does not have this method, and neither do any of its parent classes. All these are subclasses of the Error class, and you should code so that they do not occur. But when something unexpected occurs while running the app, and the code cannot cope with it, an Unhandled Exception occurs. Especially input values that are read in from the keyboard, a file, or a network connection can be dangerous. Suppose input is such a value that is supposed to be an integer (refer to exceptions.dart); we try to convert it to an int type in line (1):

var input = "47B9"; // value read from input,should be an integer
int inp = int.parse(input);                 (1)

While running the program on the console...