Question

Suppose your program contains code to create a dynamic array as in SelfTest Exercise \(10,\) and suppose the pointer variable entry has not had its (pointer) value changed. Write code to destroy this new dynamic array and return the memory it uses to the freestore. int array_size = 10; int *a; a = new int[array_size]; int i; for (i = 0; i < array_size; i++) a[i] = i; while (*a < 9) { a++; cout << *a << " "; } cout << endl;

Short answer

Answer: To modify the given code, follow these steps: 1. Decrement the pointer "a" back to the original starting point by subtracting the final value of *a from the pointer "a". 2. Delete the dynamic array with the "delete[]" keyword.

Step-by-step solution

Decrement the pointer "a" back to the original starting point

After the while loop, the pointer "a" is incremented, so we need to decrement it back to the original starting point before deleting the dynamic array. We can decrement by subtracting the final value of *a from the pointer "a" to get the original pointer address. ``` a = a - *a; ```

Delete the dynamic array

Now, we need to delete the dynamic array and return the memory to the freestore. We can use the "delete[]" keyword to delete the dynamic array. ``` delete[] a; ``` This is how the final modified code should look like: ```cpp #include using namespace std; int main() { int array_size = 10; int *a; a = new int[array_size]; int i; for (i = 0; i < array_size; i++) a[i] = i; while (*a < 9) { a++; cout << *a << " "; } cout << endl; // Step 1: Decrement the pointer "a" back to the original starting point. a = a - *a; // Step 2: Delete the dynamic array and return the memory to the rreestore. delete[] a; return 0; } ```

Key concepts

Memory Management in C++

In C++, memory management is a fundamental concept that revolves around allocating and freeing up memory as it is needed. To effectively manage memory, it's important to understand that C++ uses two key areas: the stack and the heap (often referred to as the freestore). The stack is where static memory allocation occurs, whereas the heap is used for dynamic memory allocation, where the size of the data structure can change at runtime.

When using dynamic arrays, as in the exercise, memory is allocated on the heap using the new keyword. This is an important feature for creating flexible data structures that can grow or shrink as required by the program. However, the memory assigned to such arrays is not automatically reclaimed when the array is no longer needed. Consequently, it is the programmer's responsibility to explicitly return this memory to the system using delete[], thus preventing memory leaks.

Memory leaks occur when programmers allocate memory by using new but fail to free it with delete. Over time, these leaks can cause the program to run out of memory, leading to crashes or slowed performance. Hence, a good grasp of memory management is critical for creating efficient and reliable C++ applications.

Pointer Arithmetic

Pointer arithmetic is a core aspect of C++ that allows programmers to navigate through memory locations. Since pointers represent memory addresses, performing arithmetic operations on them lets you efficiently access and manipulate data in arrays and other data structures.

Adding to or subtracting from a pointer moves it by a number of elements corresponding to the size of the data type it points to. For example, if you have an integer pointer and you increment it (a++), it points to the next integer in a block of memory, moving it by sizeof(int) bytes. Similarly, decrementing the pointer moves it backwards.

However, it's crucial to perform these operations cautiously. Going beyond bounds can lead to undefined behavior, such as accessing memory that the program is not supposed to. The exercise provides a clear demonstration of careful pointer arithmetic. After incrementing the pointer a within the while loop, the program decrements it before freeing the memory, ensuring it points back to the initial allocated memory block. Without such adjustment, the delete[] operation would not free the correct memory, potentially causing errors.

Deallocation of Memory

The deallocation of memory in C++ is an important task that removes unused memory from the heap to prevent resource waste and leaks. In the context of the given exercise, deallocation is achieved using the delete[] statement. It not only marks the previously allocated memory as free but also calls destructors for any objects that may have been created within that block of memory.

This process is particularly relevant when working with dynamic arrays, where the lifetime of the allocated memory extends beyond a single function or scope. Here's what you must understand about deallocation:

• The delete[] operator should be used for memory allocated with new[].
• Failure to deallocate can lead to memory leaks, causing the program to consume more and more memory over time.
• After deallocation, pointers should either be set to nullptr or not be used again, to avoid dangling pointers, which reference a memory location that has already been deallocated.

It's worth noting that the exercise showcases an improper pointer decrement before deallocation (a = a - *a;). The correct decrement would need to restore the pointer to its original address by keeping track of the movements or calculating the offset accurately. Otherwise, the deallocation may target the wrong address, causing undefined behavior in the program.