C++ program part4

1. What are the differences between a C++ struct and C++ class?
   The default member and base class access specifiers are different.
   This is one of the commonly misunderstood aspects of C++. Believe it or not, many programmers think that a C++ struct is just like a C struct, while a C++ class has inheritance, access specifiers, member functions, overloaded operators, and so on. Some of them have even written books about C++. Actually, the C++ struct has all the features of the class. The only differences are that a struct defaults to public member access and public base class inheritance, and a class defaults to the private access specifier and private base class inheritance. Getting this question wrong does not necessarily disqualify you because you will be in plenty of good company. Getting it right is a definite plus.
   
   
2. How many ways are there to initialize an int with a constant?
   Two.
   There are two formats for initializers in C++ as shown in Example 1. Example 1(a) uses the traditional C notation, while Example 1(b) uses constructor notation. Many programmers do not know about the notation in Example 1(b), although they should certainly know about the first one. Many old-timer C programmers who made the switch to C++ never use the second idiom, although some wise heads of C++ profess to prefer it.
   
   A reader wrote to tell me of two other ways, as shown in Examples 2(a) and 2(b), which made me think that maybe the answer could be extended even further to include the initialization of an int function parameter with a constant argument from the caller.
   
   
3. How does throwing and catching exceptions differ from using setjmp and longjmp?
   The throw operation calls the destructors for automatic objects instantiated since entry to the try block.
   Exceptions are in the mainstream of C++ now, so most programmers, if they are familiar with setjmp and longjmp, should know the difference. Both idioms return a program from the nested depths of multiple function calls to a defined position higher in the program. The program stack is "unwound" so that the state of the program with respect to function calls and pushed arguments is restored as if the calls had not been made. C++ exception handling adds to that behavior the orderly calls to the destructors of automatic objects that were instantiated as the program proceeded from within the try block toward where the throw expression is evaluated.
   It's okay to discuss the notational differences between the two idioms. Explain the syntax of try blocks, catch exception handlers, and throw expressions. Then specifically address what happens in a throw that does not happen in a longjmp. Your answer should reflect an understanding of the behavior described in the answer just given.
   One valid reason for not knowing about exception handling is that your experience is exclusively with older C++ compilers that do not implement exception handling. I would prefer that you have at least heard of exception handling, though.
   It is not unusual for C and C++ programmers to be unfamiliar with setjmp/ longjmp. Those constructs are not particularly intuitive. A C programmer who has written recursive descent parsing algorithms will certainly be familiar with setjmp/ longjmp. Others might not, and that's acceptable. In that case, you won't be able to discuss how setjmp/longjmp differs from C++ exception handling, but let the interview turn into a discussion of C++ exception handling in general. That conversation will reveal to the interviewer a lot about your overall understanding of C++.