C++ for Dummies (3rd Edition)/C_FD.iso/C__FD.EXE/C++ FD/WORKOUT/QUESTION.TXT

Text File | 1996-09-06 | 9.8 KB | 276 lines

25-Minute Workout
Part I: Questions
Just to make sure that you were paying attention, I want to ask you a few questions. ôYou
vill answer!ö (The answers are on the disk. The answer files are named according to Part
number.)
1
Declare the following. (In function declarations, assume that the functions take no
arguments.)
        a. An array of ten integers
        b. A pointer to an integer
        c. An array of ten pointers to integers
        d. A function returning a pointer to an integer
          e. A pointer to a function that takes an integer and returns nothing
2
Given that the function fn() takes an int followed by a float and returns an int, why will
the following not work?
void anotherFn()
{
   int x;
   x = fn(1, 2);
}
What can you do to make it work? Hint: DonÆt change the call in this prototypical
problem.
3
WhatÆs wrong with the following displayArray() function?
#include <stdio.h>
void displayArray(int *pArray, int number)
{
   /*arrange in two columns*/
   int i;
   int noPairs = number / 2;
   int odd = number % 2;
   for (i = 0; i < (2 * noPairs);)
   {
      printf(ôarray[%2d] = %d,  array[%2d] = %d\nö,
             i, pArray[i++], i, pArray[i++]);
   }
   if (odd)
   {
      printf(ôarray[%2d] = %d\nö, i, pArray[i]);
   }
}

int main()
{
   int array[] = {1, 2, 3, 4, 5};

   displayArray(array, 5);    /*may not generate proper
output*/
   return 0;
}
4
Write and prototype a function that accepts from the keyboard two integer values, x and y,
and returns their values in arguments passed from the calling function.
5
Assuming that you want to know the length in bytes of a particular structure, whatÆs
wrong with the following?
/*function to return size of a MyStruct*/
int sizeOfMyStruct()
{
   /*allocate an array of 2 MyStructs*/
   struct MyStruct ms[2];

   /*now return the difference of the address of
     the second element minus that of the first*/
   return &ms[1] - &ms[0];
}
Part II: Questions
Now weÆve come to my favorite part of every part, the workout. Slip on your leotards and
get out your keyboards. YouÆll have 25 minutes and no cheating.
1
    a.    Given the following macro, list any potential problems you can find
with it:
//TWO_MAX - return 2 * maximum of two numbers
#define TWO_MAX (x, y) x > y ? (2 * x) : (2 * y)
    b.    How can these problems best be avoided?
2
C++ doesnÆt allow arguments other than the last to be given default values. Thus, the
following is wrong:
 void aFunc(int x, float y = 0.0, char z) {
   cout << ôx = ô   << x
        << ô, y = ô << y
        << ô, z = ô << z
        << ô\nö;
}
Is there some way we can achieve the result we want in this example? (DonÆt overload
your brain thinking about this one.)
3
Which of the following overloaded functions are called in each of the calls in main()? If
any of the calls are ambiguous (that is, they canÆt be resolved), list all candidates:
void fn(int x) {}             //1
void fn(char *x) {}           //2
void fn(void *x) {}           //3
void fn(int x, float y) {}    //4
void fn(int x, double y) {}   //5
int main()
{
   fn(1);                     //a
   fn(ô1ö);                   //b
   int i;
   fn(&i);                    //c
   fn(æ1Æ );                  //d
   fn(1, 2);                  //e
   return 0;
}
4
The following program compiles but does not link properly. Why?
int printf(const char *, ...);
int main()
{
   printf(ôHello world\nö);
   return 0;
}
I mentioned the solution in the text, but donÆt go back and look until youÆve thought
about it.
5
In Part I, you were asked to write and prototype a function that accepts two integer
values, x and y, from the keyboard and returns them in arguments passed from the calling
function. Do it again, but this time use referential arguments. Solve the problem twice,
the first time using scanf() and the second time using stream input.
6
Let us assume the existence of a new mathematical class called Davis. (IÆll be
immortalized.) All the operations defined on real numbers are defined also on Davis.
Write the prototypes for a set of overloaded functions called multiply() that perform
multiplication between Davis numbers and Davis numbers as well as between Davis
numbers and floating-point numbers. (Note that a Davis times a Davis returns a Davis,
and a Davis times a float returns a Davis.)
7
The first program that anyone writes in C is the following ôHello worldö program:
#include <stdio.h>
int main()
{
   printf(ôHello, world\nö);
   return 0;
}
Rewrite this program to use stream output.
Part III: Questions
This part has only one exercise. The time has come to sink or swim. Write a program that
does the following.
Model a set of courses and students. Students have names. Students can enroll in courses.
Students are given a grade (between 0 and 4) in each class. Courses can have different
numbers of semester hours.
After all the students have been graded, the program should then spit out the following:
    *    The average grade in each course
    *    Each studentÆs grade in each course
    *    The studentÆs average grade for all classes
    *    The studentÆs grade in each course curved by the average of all grades
in the class
Write your solution in C++. (I didnÆt really need to say that, did I?)
Here are a few tips for solving this problem. One, use an object-oriented approach.
Protect your data members as much as possible.
Two, study the requirements to find the candidate classes. Then examine the output
requirements to determine the member functions you will need. Make CRC cards if it
helps.
Three, use the following simple curving formula:
curved grade = 3.0F * (actual grade / average)
This makes the average grade 3.0. Make sure, however, that the grade of any single
student does not exceed 4.0.
Four, concentrate on what classes you need to solve this problem. To keep the program as
short as possible, you can hardcode the actual course objects and student objects that you
will need to test your classes. Just make sure that you provide enough courses and
students to show that the classes work.
Part IV: Questions
Once again, itÆs time to start sweating. Get out your keyboards and put away your notes.
You have 25 minutes @md and no cheating.
1
    a.    Write a constructor for the class Student in the program you wrote for
the Part III Workout. (You did write that program, didnÆt you?) This
constructor should not make any restrictions on the length of the name.
Hint: Use new.
    b.    Consider the following class:
class Motor
{
   public:
     Motor(int noCylinders, float displacement);
};
class Car
{
   public:

   //this constructor is not complete
   Car(int color, float displacement,
       int noDoors = 4, int noCylinders = 6)
    {
      //stuff goes here
    }
   protected:
    Motor motor;
    int   paintColor;
    int   numberDoors;
};
        Complete the constructor for Car. DonÆt forget to initialize the member
motor.
    c.    In the following declaration of student, what constructor call is invoked
on which members?
Student otherStudent(ôDannyö);
Student student[5] = {ôRandyö, otherStudent, ôTrudyö};
    d.    What does the following do?
class Student
{
   public:
     Student(char *pName);
     Student()
     {
        Student("no name");
     }
};
    e.    Assuming that the intent in 1d was to avoid having two constructors,
how could you do this correctly? There are several ways to do this.

2
    a.    Why is the constructor Student::Student(Student) illegal? Hint: In older
versions of the compiler in which the constructor is not illegal,
invoking this constructor is always fatal.
    b.    Why was the copy constructor in BUDGET4 declared protected? Hint:
What asset is it trying to protect?
3
    a.    WhatÆs wrong with the following count() function? Hint: This is a
subtle problem.
class Student
{
   public:
    static int count;
};
int Student::count;

//count - count how many students between first and last
void count(Student *pFirst, Student *pLast)
{
   Student *pS = pFirst;
   pS->count = 0;        //start with 0
   while (pS != pLast)   //until we get to the last one
   {
     pS++->count += 1;   //count each one
   }                     //leave count with student count
    }
    b.    How many bytes of memory are used by s? (Assume that a char is one
byte and that an int is two bytes.)
class Student
{
   public:
    char name[40];
    static int count;
    };
    Student s[10];
Part V: Questions
ItÆs review time again. (Dawg!) Set that calisthenics timer and see whether you know as
much as you think you do. As always, I have provided answers in case you get stuck.
1
    a.    In BUDGET5, both account types (Checking and Savings) use the same
display function. In previous versions of BUDGET, however, savings
accounts display the number of withdrawals. Make the savings
accounts do so again. Hint: Use virtual functions and make minimal
changes to the classes.
    b.    The bank wants a new Savings account that acts just like a conventional
Savings account if the balance is below $750. If the balance stays at or
above that magical number, however, the bank wonÆt charge a fee.
Without changing the existing classes, add a new class to BUDGET5 to
handle this change.
    c.    BUDGET5 also displays Savings and Checking accounts mixed
together. Separate the two types of accounts while they are displayed,
as they were in previous versions of BUDGET. Hint: There are two
approaches here. One is to keep the two accounts in separate lists. The
second is to recognize which is which when theyÆre in the same list.
Try both approaches.

2
Factor the following concrete classes into some type of hierarchy. You will want to create
new classes to represent abstract concepts.
        Citroen CV2 (small air-cooled 2-door)
        Sedan
        Pickup
        Station wagon
        Panel truck
        18-wheeler