Beginner exception handling issue

You can yourself inherit from base Exception class to have your own Exception type or use prepared Exception class like those my friends has bring them up there. About your case you should probably need to provide an Exception based on base exception class to evaluate input first and throw the exception you write exception if did not satisfy condition your want. like this:

class myException:Exception {
...
}

int evaluateInput(input) {
 if
 ...
 else
  throw myException;
}

// Get input from user

try:
 cin>>input;
 evaluateInput(input);
catch(myException)
 doWhatYouWant;

Exceptions are handled in C++ using a try-catch block. Exception handling is one improved feature of C++ over C. Exception handling prevents programs from crashing with unknown errors.

 try
    {
         //code to be tried
    }
    catch(Exception& e)
    {
          //make user understand the problem
      throw [expression]
    }

you can read through the MSDN page Or for a basic understanding you can read this

The basic example for try catch is something like this:

try
{
    // code that throws an exception
}
catch(...)
{
    // exception handling
}

Note that the three dots are perfectly valid for catching all exceptions, though you do not know "what" you catch. This is why you should prefer specifying the type in the parentheses.

The exception to be caught can be any type beginning from int and ending with a pointer to an object that derives from a exception class. This concept is very flexible, however you must know what exception may occur.

This may be a more concrete example, using std::excpetion: Note the catch by reference.

try
{
    throw std::exception();
}
catch (std::exception& e)
{
    // ...
}

Next example assumes you write C++ with MFC libraries. It clarifies that CException catch is executed because CFileException derives from CException. The CException object deletes itself if it is not needed anymore. Unless your exception derives from CException you should not throw a pointer and stick to the example above.

try
{
    throw new CFileException();
}
catch (CException* e)
{
    // CFileException is caught
}

Last but not least this is also important: You may define several catch blocks to catch different exceptions:

try
{
    throw new CFileException();
}
catch (CMemoryException* e)
{
    // ignore e
}
catch (CFileException* e)
{
    // rethrow exception so it gets handeled else where
    throw;
}
catch (CException* e)
{
    // note that catching the base class should be the last catch
}

You can use simple if..else loop for simple user input validations. You can use exceptions in pretty similar way

e.g.

try {
      ...code that can generate the error...
   } catch (some_exception& e) {
     ...code that handles the error...
   }