In some languages, certain exceptions are known as checked exceptions and those

languages require that the exceptions are caught, but all exceptions in C$++$ are known

as unchecked exceptions, which do not require an exception handler. Most unchecked

exceptions, however, cause the program to display an error message $($which may be

a security issue since it exposes the inner details of your application$)$ and stop

execution when not handled. Others, such as problems with input$/$output$,$ must be

activated by the programmer before the runtime environment will throw them.

Exception handling provides a way for the program to possibly recover from an error

or at least terminate in a graceful manner.

Consider the following simple program and type it in as Lab$12$B $.$ cpp:

Compile and run the program, entering an integer between $1$ and $10,$ inclusively.

Hopefully, all worked well and it responded that you entered the number correctly.

The program is requesting a number, but what if the user does not cooperate? Run

the program again and enter "four". The program is unable to store an integer value

into num, so num retains its original value of $0$ and the program falls into an infinite

loop.

By default, C$++$ does not throw exceptions when something goes wrong with I$/$O$.$ We

can, however, activate exception$-$throwing by prepending the following line of code

to the start of your main $()$ function:

cin.exceptions $($ios: :failbit$)$;

This line informs C$++$ that you'd like to the program to throw iostream: : failure

exception whenever an I$/$O$-$related method fails. Try running the program again with

this line of code present and enter "four". This time, the program should terminate

and generate an error message, rather than fall into an infinite loop.