Question

a. Write a statement that declares sales to be a pointer to a pointer of type double. b. Write a C++ code that dynamically creates a two-dimensional array of five rows and seven columns and sales contains the base address of that array. c. Write a C++ code that inputs data from the standard input device into the array sales. d. Write a C++ code that deallocates the memory space occupied by the two- dimensional array to which sales points.

Short answer

Create a double pointer with `double **sales` and dynamically allocate a 5x7 array. Input values via nested loops and deallocate with `delete`.

Step-by-step solution

Declare the Pointer to a Pointer

To declare a pointer to a pointer of type double, you need to specify two asterisks in the declaration. The statement is written as: ```cpp double **sales; ```

Create a Dynamic 2D Array

First, declare the number of rows and columns. Then, allocate memory for an array of pointers (for rows) using the `new` operator. Finally, for each row, allocate memory for columns. Here's the code to create a 5x7 2D array: ```cpp int rows = 5, cols = 7; sales = new double*[rows]; for(int i = 0; i < rows; ++i) { sales[i] = new double[cols]; } ```

Input Data to the Array

Use nested loops to input data into the 2D array. The outer loop iterates over the rows, and the inner loop iterates over the columns, reading values from the standard input. ```cpp for(int i = 0; i < rows; ++i) { for(int j = 0; j < cols; ++j) { std::cin >> sales[i][j]; } } ```

Deallocate Memory

Use two loops to delete each row's allocated memory and then delete the array of pointers. This ensures all allocated memory is properly freed. ```cpp for(int i = 0; i < rows; ++i) { delete[] sales[i]; } delete[] sales; ```

Key concepts

Pointers to Pointers

In C++, pointers to pointers provide a way to manage multi-level memory addresses. A pointer to a pointer can hold the address of another pointer, offering a flexible method to manipulate data. When declaring a pointer to a pointer, for instance, of type double, you would use two asterisks. The syntax `double **sales;` declares `sales` as a pointer to a pointer of double. This additional layer is especially useful when dealing with dynamic multi-dimensional arrays, allowing direct access to memory addresses. You can visualize it as a link pointing to another link, which ultimately points to the actual data. This concept comes in handy for managing complex data structures.

Two-Dimensional Arrays

Two-dimensional arrays are akin to a table of rows and columns. They make organizing data more intuitive. In dynamic memory allocation of such arrays in C++, you first allocate memory for an array of pointers (each representing a row), and then for each row, allocate an array of actual data elements (representing columns).

The code snippet below demonstrates creating a 5x7 dynamic array:

• First, declare the size of dimensions: `int rows = 5, cols = 7;`
• Allocate memory for rows: `sales = new double*[rows];`
• Iterate through and allocate memory for each column in the rows using a loop:
  `for(int i = 0; i < rows; ++i) { sales[i] = new double[cols]; }`

Dynamic two-dimensional arrays provide flexibility as their size need not be fixed at compile time, thus, they can adapt to user inputs more efficiently.

Memory Deallocation

Deallocation of memory in C++ ensures that dynamically allocated memory, once no longer needed, is released back to the system to prevent memory leaks. Every `new` allocation requires a corresponding `delete` statement. For a dynamically allocated two-dimensional array, you first need to delete each row's memory and then the array of row pointers.

The process includes:

• Iterate through the array of pointers and free each row with `delete[] sales[i];`
• Finally, delete the array of pointers: `delete[] sales;`

In doing so, you ensure all memory blocks are returned properly, maintaining the efficiency and performance of your application. Missing out on proper deallocation can lead to memory leaks, where memory usage speedily ramps up, potentially crashing the program.

C++ Input/Output

C++ provides various ways to handle input and output operations, which are crucial for interacting with users. The standard input stream, `std::cin`, is frequently employed to gather data from the user.

For inputting data into a 2D array, nested loops facilitate iterating through each element:

• Outer loop runs through each row.
• Inner loop collects data for each column using `std::cin >> sales[i][j];`.

This approach illustrates a straightforward and efficient method to populate structures like dynamic arrays with user-specified data, making C++ a powerful language for building interactive applications. Remember, proper error handling during input operations is crucial to ensure robust applications.