Question

Consider the following statement: int *num; a. Write the C++ statement that dynamically creates an array of 10 components of type int and num contains the base address of the array. b. Write a C++ code that inputs data into the array num from the standard input device. c. Write a C++ statement that deallocates the memory space of array to which num points.

Short answer

Use `int *num; num = new int[10];` to create the array, `cin` loop to input, and `delete[] num;` to deallocate.

Step-by-step solution

Declare a pointer

The exercise already provides a declaration: `int *num;`. This statement declares a pointer named `num` which is designed to point to an integer.

Allocate memory dynamically

We use the `new` operator to allocate memory dynamically for an array of 10 integers. The following C++ statement accomplishes this: ```cpp num = new int[10]; ``` This will create an array of 10 integers and store the base address of the array in the pointer `num`.

Input data into the array

To input data into each element of the array, use a loop to iterate over the array and use `cin` to read values from the input. Here's a sample code snippet to fill the array with data: ```cpp for (int i = 0; i < 10; ++i) { std::cin >> num[i]; } ``` This loop ensures all 10 integers can be filled with data from user input.

Deallocate memory

To deallocate the memory which was previously allocated for the array, use the `delete[]` operator. This is how you write the statement: ```cpp delete[] num; ``` This statement will free the memory space of the array pointed to by `num`, thereby preventing any memory leaks.

Key concepts

Pointer Declaration

In C++, pointers are a fundamental concept for managing memory efficiently. A pointer is essentially a variable that holds the address of another variable. When you declare a pointer, you define its capability to point to a specific data type. For example, the statement `int *num;` declares a pointer named `num` that is designed to point to an integer type variable. When the compiler encounters this declaration, it reserves space to store a memory address that will point to an integer variable.

• The asterisk `*` character is used in the declaration to signify that `num` is a pointer.
• The type preceding the asterisk indicates the type of data the pointer will point to—as in this example, an integer.
• This declaration does not allocate memory to store the integers, it simply sets aside space to store the address of an integer value.

Pointers are powerful because they enable dynamic memory allocation, which allows programs to request memory storage at runtime rather than compile time.

Array Input and Output

In C++, handling arrays involves managing groups of variables through a single identifier. Once you have a pointer that holds the base address of an array, as in `int *num;`, you can easily input and output data from and to the array using loops.
Let's assume you have dynamically allocated an array of 10 integers using `num = new int[10];`. To fill this array with user input, iterate over each element with a loop and use the `std::cin` input stream:
```cpp for (int i = 0; i < 10; ++i) { std::cin >> num[i]; } ``` This loop runs 10 times, allowing input from the user to each position within the array.

• `std::cin` reads inputs directly from the keyboard, one at a time, placing them into the array `num`.
• The `[]` operator is used to access the elements of the array.
• Remember that the loop index `i` runs from 0 to 9, corresponding to the 10 elements of the array.

Outputting data uses a similar loop with `std::cout` for displaying values, showcasing how array manipulation can be set up through standard input and output streams.

Memory Deallocation

Efficient memory management in C++ is crucial, and it involves both allocating and deallocating memory. Memory that is dynamically allocated using the `new` operator must be manually de-allocated using the `delete` operator.
When you dynamically allocate an array, as done with `int *num = new int[10];`, it is vital to free up that memory once it is no longer needed. Ignoring this step leads to memory leaks, where unused memory remains allocated, eventually causing the program to run out of memory.
To deallocate the memory pointed to by the pointer `num`, you would use: ```cpp delete[] num; ```

• The `delete[]` operator tells the program to release the memory allocated for an array block.
• The square brackets `[]` are important as they signify that an array is being deallocated.
• After deallocating, the pointer `num` becomes a dangling pointer, meaning it points to some undefined memory location. Thus, it's a good practice to set the pointer to `nullptr` afterwards, making it clear it no longer points to valid data.

C++ Operators

C++ includes a variety of operators that serve different functions essential to programming. When dealing with dynamic memory allocation, several operating techniques are highlighted:

• New Operator: Used for dynamic memory allocation. For example, `new int[10]` allocates space for an array of 10 integers.
• Delete Operator: Frees memory that was dynamically allocated. When done, use `delete[]` for arrays, as in `delete[] num;`.
• Indirection Operator `*`: Used to declare pointers and access the value stored in the memory pointed to by the pointer.
• Address-of Operator `&`: Provides the address of a variable, commonly used to initialize a pointer.

Understanding these operators enhances a developer's ability to manage memory effectively and manipulate data with precision. Using them correctly helps avoid common pitfalls such as memory leaks, undefined behavior, and unwanted program crashes.