CS 12400 (MW) Exam 2 Review

The exam is on Wednesday, April 5.

The exam is over Chapters 6 and 7 from the textbook,
https://learn.zybooks.com/zybook/PurdueNorthwest-HammondCS124KraftSpring2023

Here are the sections that we covered from those two chapters.
   Sections 6.1, 6.3, 6.7, 6.9, 6.10, 6.11, 6.12, 6.13, 6.14.
   Sections 7.1, 7.2, 7.3, 7.4, 7.6, 7.7, 7.8, 7.9, 7.10, 7.11, 7.12.


Here is a list of topics that we covered.
  1) C++ arrays.
  2) Array algorithms.
  3) Arrays as function parameters.
  4) Two-dimensional arrays.
  5) Pointers and the "address of" operator.
  6) Pointers vs. C++ references.
  7) Pointers and arrays,
     a) pointer arithmetic,
     b) arrays decay to pointers,
     c) the "const" keyword (read-only arrays).
  8) C and C++ strings.
  9) Dynamic memory allocation,
     a) the "new" operator,
     b) dynamic arrays,
     c) the "delete" and "delete[]" operators,
     d) functions that return (dynamic) arrays.
 10) Arrays of pointers.



Here are a few review problems.


1.) Write a definition for a function that takes an integer
array as a parameter (along with its size) and fills the
array with -1's.



2.) Write a definition for a function that takes two integer
arrays as parameters (along with their sizes) and copies the
values of the shorter array into the longer array. The function
should not assume that either the first or the second array
parameter is the shorter one. If the arrays have equal size,
copy the first array parameter into the second array parameter.



3.) Given the array declaration

    int my_array[4][4];

what element of the array does the following
expression refer to? Briefly explain your answer.

    my_array[1][7];



4.) Consider the following code fragment.

    int n = 5;
    int *p1 = &n;
    int a[] = {21, 22, 23};
    int *p2 = &( a[1] );
    int *p3;
    int **p4 = &p3;
    *p4 = a + 2;
    *p2 = -1;
    **p4 = -2;

Draw a picture that represents the state of all the
memory locations used by the code fragment when the
fragment has finished executing. Your picture should
look like the memory drawings made by the C++ Tutor,
https://pythontutor.com/visualize.html



5.) Consider the following program segment.

    char a[] = "Mary had a little lamb";
    char *p = a;
    int count = 0;
    while (*p == ' ') ++p;
    while (*p != '\0')
    {
       ++count;
       while (*p != ' ' && *p != '\0') ++p;
       while (*p == ' ') ++p;
    }

  (a) With the given value for a, what is the value of count at the
      end of the outer while-loop? For an arbitrary string stored in
      array a, what is the value of count at the end of the outer
      while-loop?
  (b) What is the purpose of the first inner while-loop?
  (c) What is the purpose of the second inner while-loop?
  (d) What is the purpose of the very first while-loop (the
      one just before the outer while-loop)?



6.) Suppose we want to write a function that takes as an input
a one dimensional "partially filled array." Why would it be a
good idea for the function to also have two other integer
parameters, for example:

   int doSomething(int partiallyFilledArray[], int m, int n);



7.) It is easy to create an array in C++.

   int arrA[10];

Why do we need this more complicated way to create arrays?

   int *arrB = new int[10];



8.) Write the definition of a function with the following declaration.

    char* reverse(const char str[]);

The goal of this function is to return (a pointer to) a C string
that contains the reverse of the C string contained in its parameter
str. Your function definition will need to do four steps. First,
compute the length of the C string str. Second, create a dynamic
array, of the proper size, that will hold the reversed string.
Third, copy the contents from str into the dynamic array in reverse
order (make sure your new C string really is a C string). Finally,
return a pointer to the dynamic array. Your function should
explicitly write the code to do these steps without making use of,
or calling any, library functions.



9.) Each of the following two for-loops has a problem. What
is the problem for each loop? How might you fix each loop?

    int arr1[] = {5, 4, 3, 2, 1, 0};
    const int * arr2 = arr1;

    for (int i = 0; i < 6; ++i)
    {
       arr2[i] += 10;
    }

    for (int * const p = arr1; p < arr1 + 6; ++p)
    {
       *p += 10;
    }




10.) Suppose you have a function declared as

    int doSomething(const int inputArray[]);

and in the body of the function doSomething there is a line like this.

    int k = doSomeMore(inputArray[i]);

What must be true about the declaration of the function doSomeMore
in order for this line to compile? Briefly explain why.



11.) Given the following declarations,

    int i = 3;
    int *ip = new int(-3);
    int a[10];

what are the types of each of the following expressions?
In other words, for each expression, if you needed to
declare a variable that could hold the value of the
expression, what type would the variable need to have?
  (a)  i
  (b)  &i
  (c)  ip
  (d)  *ip
  (e)  &ip
  (f)  a
  (g)  ip[0]
  (h)  ip + 3



12.) Consider the following code fragment.

    int *p1;
    int *p2;
    p1 = new int;
    p2 = new int;
    *p1 = 10;
    *p2 = 20;
    cout << *p1 << " " << *p2 << endl;
    *p1 = *p2;
    cout << *p1 << " " << *p2 << endl;
    *p1 = 30;
    cout << *p1 << " " << *p2 << endl;
    p1 = p2;  // Draw a picture at this point.
    cout << *p1 << " " << *p2 << endl;
    *p1 = 40;
    cout << *p1 << " " << *p2 << endl;

(a) What is the output produced by this code fragment?
(b) For the line "p1 = p2;", draw a picture that represents at that
point in the code fragment the state of all the memory locations used
by the code fragment. Your picture should look like the memory
drawings made by the C++ Tutor, https://pythontutor.com/cpp.html