The following C++ main driver, along with function myFunc, uses a C++ class DynA

ID: 3805173 • Letter: T

Question

The following C++ main driver, along with function myFunc, uses a C++ class DynArray that models a dynamic integer array – that is, the class uses dynamic memory allocation to create a contiguous block of memory for storing a specified number of integers. The indexing for a DynArray object is the same as for a regular array. But, a DynArray can be initialized to size zero.

Write the C++ DynArray class. Here is a brief description of all of the class functions that your class should include:

No-argument constructor – initializes a DynArray object to being empty.

One-argument constructor – uses dynamic memory allocation to obtain a contiguous block of memory for storing n int values, where n is its argument.

show – displays the nth element in the DynArray. If the DynArray is empty or if n is an invalid index, this function should generate an error message.

set – will set the nth element in the DynArray to x, where n is the value of its first argument and x is value of its second argument. If the DynArray is empty or if n is an invalid index, this function should generate an error message.

expand – will take an existing DynArray and expand its size by its argument, s. Hint: To expand a DynArray, allocate a new, larger block of dynamic memory, copy the values from the old DynArray to the new memory, and deallocate the old memory.

A destructor to deallocate dynamic memory when a DynArray object passes out of scope.

Requirement: When accessing the dynamic array elements in the set, show and expand member functions, you must use the dereferencing operator, *, along with pointer arithmetic instead of the array indexing operator, [].

Next, combine your DynArray class with the following main and myFunc code and run the resulting C++ program. The output generated from a run of your program should be similar to that shown in the output of a sample run given after the code.

void myFunc();

int main()

{

int size,more,i;

DynArray y;

cout << "Enter dynamic array size: ";

cin >> size;

DynArray x(size);

for(i=0;i<size;i++)

x.set(i,3*i);

for(i=0;i<size;i++)

x.show(i);

cout << "How much more dynamic array space do you want? ";

cin >> more;

x.expand(more);

for(i=0;i<(size+more);i++)

x.set(i,5*i);

for(i=0;i<(size+more);i++)

x.show(i);

x.show(size+more+5); //invalid index in show

x.set(-2,9); //invalid index in set

y.set(3,6); //empty DynArray set

y.show(3); //empty DynArray show

myFunc();

char ch; cin >> ch;

return 0;

}

void myFunc()

{

int i;

cout << "hi from myFunc... ";

DynArray y(5);

for(i=0;i<5;i++)

y.set(i,i*i);

for(i=0;i<5;i++)

y.show(i);

cout << "bye from myFunc... ";

}

Output from a sample run of the program (user input is in bold):

Enter dynamic array size: 3

How much more dynamic array space do you want? 2

Invalid index in show

Invalid index in set

Cannot set - DynArray empty

Cannot show - DynArray empty

hi from myFunc...

bye from myFunc...

hi from the DynArray destructor...

Explanation / Answer

#include <iostream>

using namespace std;

class DynArray
{
private:
int size;
int capacity;
int *arr;

public:
DynArray()
{
arr = new int[0];
capacity = 0;
size = 0;
}

DynArray(int n)
{
arr = new int[n];
capacity = n;
size = 0;
}

void show(int n)
{
if (n >= 0 && n < size)
{
cout << "Element " << n << " is "<<*(arr + n) << endl;
}
else
{
if (size == 0) cout << "Cannot show - DynArray empty" << endl;
else cout << "Invalid index in show" << endl;
}
}

void set(int n, int x)
{
if (n >= 0 && n < capacity)
{
*(arr + n) = x;
size++;
}
else
{
if (size == 0) cout << "Cannot set - DynArray empty" << endl;
else cout << "Invalid index in set" << endl;
}
}

void expand(int s)
{
int *temp = new int[capacity + s];
capacity = capacity + s;
for(int i = 0; i < size; i++)
{
*(temp + i) = *(arr + i);
}

delete arr;
arr = temp;
}

~DynArray()
{
cout << "hi from the DynArray destructor..." << endl;
delete arr;
}
};

void myFunc();
int main()
{
int size,more,i;
DynArray y;
cout << "Enter dynamic array size: ";
cin >> size;
DynArray x(size);
for(i=0;i<size;i++)
x.set(i,3*i);
for(i=0;i<size;i++)
x.show(i);
cout << "How much more dynamic array space do you want? ";
cin >> more;
x.expand(more);
for(i=0;i<(size+more);i++)
x.set(i,5*i);
for(i=0;i<(size+more);i++)
x.show(i);
x.show(size+more+5); //invalid index in show
x.set(-2,9); //invalid index in set
y.set(3,6); //empty DynArray set
y.show(3); //empty DynArray show
myFunc();
char ch; cin >> ch;
return 0;
}
void myFunc()
{
int i;
cout << "hi from myFunc... ";
DynArray y(5);
for(i=0;i<5;i++)
y.set(i,i*i);
for(i=0;i<5;i++)
y.show(i);
cout << "bye from myFunc... ";
}

// sample run