Topical Information

The purpose of this quiz is to give you a chance to focus your knowledge of simple classes in C++.

Question Set Information

Questions

  1. (Briefly) Define the following object-oriented terms:

    class

    
The C++ way to implement an
ADT.  A class typically
consists of data and functions
which together represent the
data type.
    		ADT

    
Abstract Data Type:  a
generic, abstracted
description of a type of data
typically used to implement
the data type for programming
purposes but also useful
mathematically.
    object

    
A variable of a class data
type.  Also any instance —
example — of a class within a
program.  (This would include
temporary and anonymous
values, too.  And, of course,
some objects may be held
constant for a time during
program execution.)
    		member variable

    
A piece of data that makes up
part of a class' description.
A variable declared as part of
a class data type.  Member
variables are typically placed
in the private section of a
class.
    method

    
A function that makes up part
of a class' description.  A
function declared as part of a
class data type.  Methods may
be in either the public
(mostly) or the private
(sometimes) section of the
class.
    		access specifier

    
A keyword specifying what
parts of the program are
allowed to see/use/access
certain members of a class.
The two access specifiers we
learned about are private
(which is the default state
for any class member) and
public.
    constructor ('ctor')

    
A special class method which
is automatically called to
initialize a class object's
member variables when an
instance is created by the
program[mer] somehow.  All
constructors are overloaded
based on the name of the class
for which they construct.
Differing argument lists
therefore lead to different
initialization patterns — or
perhaps stem from the need for
them.  (Constructors may be
explicitly called as well.
This leads to anonymous
objects — perhaps to be used
during RVO...)
    		accessor

    
A class method allowing
programmers outside the class
to retrieve a copy of the
current value of one of the
class object's [private]
member variables.
    mutator

    
A class method allowing
programmers outside the class
to request controlled change
of a class object's [private]
member variable(s).  The key
is that error checking is
embedded (or at least
consistently called for from)
the mutators.  Any change the
program wants to make to the
class member variables should
go through the appropriate
mutator.  This will ensure all
member variables stay valid
throughout their lifetime.
    		member access operator

    
The dot (.) operator which is
used with an explicit class
object to use/access one of
its members (either variable
or function).  The object's
identifier comes first, then
the dot, and then the desired
member's identifier.  (If the
member is a function,
parentheses and arguments
would be useful at this point.
*grin*)

  2. A default constructor places values in an object's data when the programmer declaring the object fails to do so. A initialization/parameterized/unnamed constructor fills in values supplied by the programmer. (If the latter has only one input, the syntax can take one of two forms: className object = value; — like the built-in types are normally initialized — or className object (value); — which is more obviously a method call.) Finally, a copy constructor fills in values from a previously constructed object. (This constructor, too, can use both the above syntaxes. It is also called in several other places than normal variable declaration.)

  3. Name three of the most important benefits that classes give us over the built-in types.

    

      

    1. Combine multiple values into a single
    variable.
      2. 

    2. Primitive data security with private and public access
    specifiers.
      3. 

    3. Automatic/Configurable initialization with
    constructors.
      4.

  4. classes are the C++ mechanism for implementing _____. Basically this is a way to describe an entity from the real world to the computer so that we can use it in our program as a _____ to represent our data.

    1. structures, containerNO
    2. arrays, groupingNO
    3. loops, meansNO
    4. ADTs, typeOKAY
    5. overloading, constructionNO

  5. A class is supposed to be a _____ description of all the objects in a group/set. Because of this re-useful-ness, classes are often placed in _____. The class definition goes in the _____ file, while the definitions of its methods go in the associated _____ file.

    1. simplified, braces, top of the, end of theNO
    2. (actually blank), C++ programs, main, libraryNO
    3. generic, libraries, interface, implementationOKAY
    4. detailed, closets, flip, indexNO
    5. broad, programs, source, objectNO
  6.  
    TRUE✓FALSE✗ The methods of a class are supposed to emulate the built-in data types.
    TRUE✓FALSE✗ Toward this end, a class' input method behaves similarly to how cin would act on a char or short variable.
    TRUE✗FALSE✓ This means that we should always prompt the user before reading their data (within the input method).
    TRUE✓FALSE✗ Output methods should likewise behave as cout would when printing a double or long variable.
    TRUE✗FALSE✓ This means that we should always label the output data to help the user understand what's being printed (within the output method).

  7. A private keyword (which is optional/assumed) can be placed in a class declaration to show that certain parts of the class cannot be accessed from outside the class. The public keyword is placed to show that following items may be accessed from inside or outside the class. Both of these keywords must be followed by a colon (:) symbol.

  8. What is the purpose of accessor methods in a class? Are they used more by the class itself or by non-class functions? Why must we create them?

    
Accessor methods are for the retrieval of copies
of member variable data.  They are used more by
the non-class parts of the program.  We have to
create them because the data is in the private
area of the class and cannot be directly
used/seen.

    Give a particular situation where accessors would prove useful.

    
Whenever the programmer using our class wants to
do something beyond what we planned for them.
Maybe plotting a 2D point on the graphics screen.
Maybe numerically integrating a polynomial whose
coefficients we hold.  Maybe just a prettily
labeled output format rather than the typical
plain and non-labeled output format a class mostly
likely provides.

  9. What is the purpose of mutator methods in a class? Are they used more by the class itself or by non-class functions? Why must we create them?

    
Mutator methods allow for controlled change of
member variables of a class.  They are used by
anyone wanting to change a member variable!  Since
data members are typically private in our class
designs, they cannot be changed directly from
outside the class.  (And from inside the class we
of course depend on the embedded error checks to
keep our data valid at all times.)

    Give a particular situation where mutators would prove useful.

    
Any time the programmer using our class wants to
modify their object's data in a way we did not
anticipate during our design.  Maybe taking a 2D
point's coordinates from a mouse click.  Maybe
taking the derivative of a polynomial whose
coefficients we hold.  Maybe just a prettily
prompted input format rather than the plain,
non-prompted input format the class most likely
provides.
  10.  
    TRUE✓FALSE✗ Constructors are used to fill in data values during the declaration of a class object.
    TRUE✗FALSE✓ There are two basic types of constructors.
    TRUE✗FALSE✓ One is used just like with the built-in data types to fill in default values when none are supplied by the programmer.
    TRUE✓FALSE✗ Another is used when the programmer does supply default value(s) for the object's data.

  11. Name the three places/times where/when a copy constructor is automatically called by the compiler.

    1. 
When creating a new object as an exact copy of an
old object.

    
    2. 
When passing a formal argument by value it is copy
constructed from the actual argument.

    
    3. 
When returning by value from a function, the value
returned is copy constructed from the expression
result in the return statement.