Question

Suppose your program contains code to create a dynamic array as follows: int *entry; entry = new int[10]; so that the pointer variable entry is pointing to this dynamic array. Write code to fill this array with ten numbers typed in at the keyboard.

Short answer

Answer: First, initialize the dynamic array of size 10 using the "new" keyword, and include the iostream library for input functionality. Create a for loop that iterates through the array indices from 0 to 9. Inside the loop, get user input using "std::cin" and store it in the dynamic array at the current index. Finally, remember to delete the allocated memory when done.

Step-by-step solution

Initialize array and input stream

To get user input, we need to include the iostream library and use the "std::cin" object. We can initialize the pointer variable entry to point to the dynamic array, as provided in the exercise. Also, include the iostream header to enable input functionality. ```cpp #include int main() { int *entry; entry = new int[10]; } ```

Create a loop to iterate through array indices

We will use a "for" loop to iterate through all the 0-9 indices, and at each step, ask the user to provide a number. ```cpp for (int i = 0; i < 10; i++) { // Code to get input and store it in the array } ```

Get user input and assign it to array elements

Now, inside the loop we will ask the user to provide a number and store it in the "entry" array at index "i". We will use "std::cin" to get user input. ```cpp std::cout << "Enter number " << i + 1 << ": "; std::cin >> entry[i]; ```

Final code

Combining all the steps, this is the final code: ```cpp #include int main() { int *entry; entry = new int[10]; for (int i = 0; i < 10; i++) { std::cout << "Enter number " << i + 1 << ": "; std::cin >> entry[i]; } // Remember to delete the allocated memory when done delete[] entry; return 0; } ``` This code creates a dynamic array of size 10, takes user input for each element, and stores the input in the corresponding array index.

Key concepts

Pointer Variables

Pointer variables in C++ serve as a fundamental mechanism for accessing and managing memory locations. Simply put, a pointer is a variable designed to store the address of another variable. This helps in manipulating data stored at different memory addresses without having to know the variable's name.

For instance, in the exercise, int *entry; declares entry as a pointer to an integer. When entry is later assigned using new int[10];, it points to the first element of a newly allocated, 10-integer array in dynamic memory. With pointers, you gain control and flexibility over the array management and other data structures. However, remember that with great power comes great responsibility! Proper usage and deallocation of memory pointed to by pointers are essential to avoid memory leaks.

User Input

To make a program interactive, C++ utilizes user input, allowing users to provide data while the program runs. Usually accomplished using the iostream library and the std::cin object, user input can be easily captured and used within your program.

In our exercise, user input is taken ten times in a loop to fill a dynamic array. The process involves prompting the user and then waiting for the user's input to be entered into the console. The entered data is then stored in the corresponding position within the dynamic array, making std::cin a powerful tool for real-time data collection and manipulation in C++.

For Loop in C++

The for loop is a cornerstone of iterative control structures in C++. It allows the execution of a block of code multiple times, with a clear start, end, and increment for iteration. The syntax is typically: for (initialization; condition; increment) { /* code */ }.

In the context of the exercise, a for loop is used to iterate over the array indices and fill them with user input. By initializing i to 0 and continuing while i is less than 10, we cover all ten indexes of our dynamic array. Incrementing i by 1 at each step moves us through the array entry, ensuring each element is addressed.

Memory Allocation

In C++, memory allocation plays a pivotal role in managing resources for your program's needs. Dynamic memory allocation, particularly, allows you to request memory during runtime, using operators like new and delete.

When you allocate memory using new, you are reserving space in the heap. The decision of how much memory to allocate can be made based on user input or program conditions. In our exercise, new int[10] allocates memory for an array of ten integers. It's crucial to free this memory with delete[] once it's no longer needed to prevent memory leakage, which is just as important as the initial allocation.

Iostream Library

The iostream library in C++ is a standard library for input and output (I/O) operations. It's integral for reading data from the user (input) and displaying data to the user (output). The library contains familiar objects like std::cout for output to the standard output (usually the screen), and std::cin for input from the standard input (usually the keyboard).

Effective use of the iostream library is demonstrated in our exercise, where std::cout is used to prompt the user to enter a number, and std::cin is utilized to receive each number for the dynamic array. This library is included in your program by adding the line #include at the beginning of your source file.