Programming Project: Character and Integer Pointers

Programming Project: Character and Integer Pointers
Download the file CharIntPointers_incomplete.cpp.
Build and execute the program.
The output will be similar to the following:
The program dynamically allocates two arrays, one of type character and one of type
integer:
 const int ARRAY_SIZE = 10;
 const int LAST_ARRAY_ELEM_INDEX = 9;

 char* p_aChars = new char[ARRAY_SIZE];
 int* p_aIntegers = new int[ARRAY_SIZE];
The arrays are initialized using a “brute force” approach:
// Initialize character array
 p_aChars[0] = 'A';
 p_aChars[1] = 'B';
 p_aChars[2] = 'C';
 p_aChars[3] = 'C';
 p_aChars[4] = 'E';
 p_aChars[5] = 'F';
 p_aChars[6] = 'G';
 p_aChars[7] = 'G';
 p_aChars[8] = 'I';
2
 p_aChars[9] = 'J';

 // Initialize character array
 p_aIntegers[0] = 100;
 p_aIntegers[1] = 101;
 p_aIntegers[2] = 102;
 p_aIntegers[3] = 103;
 p_aIntegers[4] = 104;
 p_aIntegers[5] = 105;
 p_aIntegers[6] = 106;
 p_aIntegers[7] = 107;
 p_aIntegers[8] = 108;
 p_aIntegers[9] = 109;
They are then printed out using two while loops. For example, here is the while loop used
to print out the character array:
 char* p_c = p_aChars; // Same as p_c = &(p_aChars[0]);
 while (p_c <= &(p_aChars[LAST_ARRAY_ELEM_INDEX])) {
 std::cout << "p_c: " << static_cast<void*>(p_c)
 << ": *p_c: " << *p_c << std::endl;
 p_c++; // Increment the pointer (to point to next array element)
 }
Step 1
Comment out the brute force code to initialize the arrays and replace it with two
while loops, one while loop to initialize the character array and one to initialize the
integer array.
To quickly comment out the brute force initialization code, surround the code using the
#if 0 and #endif preprocessor directives:
#if 0
 // Initialize character array
 p_aChars[0] = 'A';
 p_aChars[1] = 'B';
 p_aChars[2] = 'C';
 p_aChars[3] = 'C';
 p_aChars[4] = 'E';
 p_aChars[5] = 'F';
 p_aChars[6] = 'G';
 p_aChars[7] = 'G';
 p_aChars[8] = 'I';
 p_aChars[9] = 'J';

 // Initialize character array
 p_aIntegers[0] = 100;
 p_aIntegers[1] = 101;
 p_aIntegers[2] = 102;
3
 p_aIntegers[3] = 103;
 p_aIntegers[4] = 104;
 p_aIntegers[5] = 105;
 p_aIntegers[6] = 106;
 p_aIntegers[7] = 107;
 p_aIntegers[8] = 108;
 p_aIntegers[9] = 109;
#endif
The code will now not be seen by the compiler; the C preprocessor removes it before the
intermediate file is presented to the compiler.
Step 2
Next, place your while loop that initializes the character array at the location
identified by a TODO comment:
// TODO: Write a while loop that initializes the values of the array pointed to by p_aChars
// Use pointer p_c. In the loop use *p_c = value
// You may need to introduce additional variables such as char c = 'A'
// INSERT WHILE LOOP HERE
Note that you can do the following:
c = ‘A’;
c++;
The value of c will be ‘B’.
Make sure that you use the * pointer de-referencing operator (e.g. *p_c) when assigning
values into the array.
Observe that the value of p_c is set to the first element of the character array just above
the place where you insert your while loop:
char* p_c = p_aChars; // Same as p_c = &(p_aChars[0]);
Step 3
Finally, place your while loop that initializes the integer array at the location
identified by a TODO comment:
// TODO: Write a while loop that initializes the values of the array pointed to by p_aIntegers
// Use pointer p_i.In the loop use *p_i = value where value is 'A', 'B', etc.
// You may need to introduce additional variables such as int i = 100.
// INSERT YOUR WHILE LOOP
4
Observe that the value of p_i is set to the first element of the integer array just above the
place where you insert your while loop:
int* p_i = p_aIntegers; // Same as p_i = &(p_aOrdinals[0]);
Step 4
Build and run your program.
The output of the program should appear nearly identical to your first run except that the
values of the addresses (p_c and p_i) may be different:
The values of the pointers (which are addresses) are given in hexadecimal (base 16).
Note that the values of p_c (the pointer to character) increase by 1 each time as p_c is
incremented using p_c++:
p_c: 0000029F8D5B9070: *p_c: A
p_c: 0000029F8D5B9071: *p_c: B
p_c: 0000029F8D5B9072: *p_c: C
p_c: 0000029F8D5B9073: *p_c: D
…
However, the values of p_i (the pointer to integer) increase by 4 each time p_i is
incremented using p_i++:
p_i: 0000029F8D5BE5A0: *p_i: 100
p_i: 0000029F8D5BE5A4: *p_i: 101
5
p_i: 0000029F8D5BE5A8: *p_i: 102
p_i: 0000029F8D5BE5AC: *p_i: 103
…
Step 5
Why do character pointers increment their address by 1 yet integer pointer
increment their address by 4?
Place your answer in the Canvas comments box.
Note that the pointer values are 48 bits, even though the program is compiled as a 64-bit
application and run on a 64-bit Windows machine. Extra Credit if you can explain
why.
Notes
You may have noticed the use of a static_cast<void *> in the while loop that outputs the
character array.
while (p_c <= &(p_aChars[LAST_ARRAY_ELEM_INDEX])) {
 std::cout << "p_c: " << static_cast<void*>(p_c) << ": *p_c: " << *p_c << std::endl;
 p_c++; // Increment the pointer (to point to next array element)
 }
The character pointer is cast to a void * pointer because character pointers have “special
meaning” to cout and must be cast to a different type of pointer, and that different type of
pointer is a void * pointer. Character pointers are treated as C strings by cout and must be
cast to override that interpretation.