Question

Look at the following array definition. int set[10]; Write a statement using pointer notation that stores the value 99 in set[7];

Short answer

Answer: You can store the value 99 in the 7th index of the array using the expression `*(set + 7) = 99;`. This expression uses pointer arithmetic and the dereference operator to access and modify the element at the desired index in the array.

Step-by-step solution

Understand pointers and arrays

In C++ and other programming languages, pointers are a way to store the address of a variable rather than its value. In the case of arrays, the array name is actually a pointer to the first element in the array. Thus, pointer arithmetic can be used to access and modify the elements of the array. In this case, let's find how to access the element at index 7 (8th element) using pointer notation.

Find the pointer to the 7th index

To find the pointer to the element at index 7, we can use pointer arithmetic. Since the pointer `set` points to the first element of the array, to get to the 7th index, we need to add 7 to the pointer. The expression to get the pointer to the 7th index is `(set + 7)`.

Use pointer notation to store the value 99 in set[7]

Now that we have the pointer to the element at index 7, we can use the dereference operator `*` to access the value stored at that pointer and assign the value 99 to it. The statement using pointer notation that stores the value 99 in set[7] is: ```cpp *(set + 7) = 99; ```

Key concepts

C++ Programming

C++ is a highly versatile and capable programming language, especially known for its ability to perform low-level memory manipulation. This feature is essential for high-performing applications. In C++, variables hold data of different types, and pointers are one variety of such variables. A pointer holds the memory address of a variable, offering a way to indirectly manipulate the actual data. Understanding pointers is crucial because they offer a level of control and efficiency in C++ that's not as directly accessible in higher-level languages.

Pointers are used for dynamic memory allocation, implementing data structures (like linked lists and trees), and for array handling, among other things. When dealing with arrays, pointers can simplify the code by reducing the need for indices, thus providing a different perspective on how to interact with the elements of an array.

Pointers and Arrays

Array Name as a Pointer

In the context of arrays, the array name, such as set in the exercise, represents the address of the first element of the array. It's important to note that this is implicitly considered to be a pointer. Knowing this opens up the possibility to use pointer notation to access elements within the array.

Dereferencing Pointers to Access Array Elements

By dereferencing the array pointer—that is, using the asterisk (*) operator—you can access the value at a specific memory address. This action is akin to accessing array elements using the subscript notation but gives you more direct control and can sometimes offer performance benefits.

The relationship between pointers and arrays in C++ emphasizes the convenience and flexibility in managing contiguous memory spaces, such as those used by arrays. When a programmer understands how to seamlessly interchange the use of pointers and array indexing, they gain a powerful tool for writing concise and efficient code.

Pointer Arithmetic

Manipulating Pointers

The concept of pointer arithmetic is tied closely with C++’s capability to manipulate the memory addresses that pointers represent. With pointer arithmetic, you can perform operations like addition or subtraction to navigate through memory locations.

When you add an integer to a pointer, you're essentially moving to a new memory location that's a certain number of elements away from the current one. The size of the step depends on the data type the pointer refers to. For example, adding one to an int pointer moves it to the next integer in memory, which is typically four bytes ahead on most systems.

Accessing Array Elements with Pointer Arithmetic

In our exercise with the set array, to access the element set[7], pointer arithmetic is used to move 7 integer locations away from set (which is a pointer to set[0]). The expression *(set + 7) first finds the address of set[7] and then dereferences it to access or modify the value at that address, just as shown in the step by step solution.