Question

Write a function void switchEnds (int *array, int size); that is passed the address of the beginning of an array and the size of the array. The function swaps the values in the first and last entries of the array.

Short answer

Question: Write a short answer describing how the switchEnds function works. Answer: The switchEnds function takes a pointer to the beginning of an array and the size of the array as input parameters. The function initializes two pointers to access the first and last elements of the array. It then uses a temporary variable to store the value of the first element, updates the first element with the value of the last element, and finally assigns the temporarily stored value to the last element, effectively swapping the values of the first and last elements in the array.

Step-by-step solution

Function signature

Write the function signature for switchEnds as follows: ```cpp void switchEnds(int *array, int size); ``` This syntax indicates that the function takes a pointer to an int (int *array) and an int (int size) as input, and returns nothing (void).

Access first and last elements

In the function body, initialize two pointers, one for the first element and one for the last element, using array and size: ```cpp int *firstElem = array; int *lastElem = array + size - 1; ```

Swap the values

Use a temporary variable to store the value in the first element, then set the value of the first element to be the value in the last element and assign the temporarily stored value to the last element: ```cpp int temp = *firstElem; *firstElem = *lastElem; *lastElem = temp; ```

Complete the function

Combine all the steps along with the function signature to create the complete switchEnds function: ```cpp void switchEnds(int *array, int size) { int *firstElem = array; int *lastElem = array + size - 1; int temp = *firstElem; *firstElem = *lastElem; *lastElem = temp; } ```

Key concepts

Function Signature

Understanding the function signature in C++ is crucial when you're learning how to manipulate arrays or perform any other tasks. A function signature consists of the function's name, return type, and parameter list. In the context of the exercise given, void switchEnds(int *array, int size); is the function signature.

Here, 'void' signifies that the function does not return a value. It's a signal that the function's role is to perform an action, rather than calculate a value to be assigned or used. The 'switchEnds' is the name of the function, which suggests the action it performs—switching the ends of an array.

In the parameters, int *array indicates that the function expects a pointer to an integer, which is the start of the array. The 'size' parameter is just an integer telling the function how many elements are in the array. Additionally, when a function's parameter list includes a pointer, it implies that the function may modify the contents of the array pointed to, as it has access to its memory location directly.

Pointer Arithmetic

Pointer arithmetic is the set of operations that C++ allows on pointer values. Despite its name, pointer arithmetic respects the size of data types. In the given solution, pointer arithmetic is used to access the last element of the array: int *lastElem = array + size - 1;.

This operation doesn't simply add one to the pointer's value; it increments the pointer by the size of the type it points to, 'int' in this case, multiplied by (size - 1). For example, if one int occupies 4 bytes in memory, and size is 5, the last element pointer will be incremented by 4 bytes times (5 - 1), positioning it at the start of the last integer of the array.

This approach works because arrays in C++ are stored in contiguous memory locations, meaning that each subsequent element in the array is located at the memory address of the previous element plus the size of that element. It's a fundamental concept in C++ that gives a programmer direct access to memory, which can optimize for speed and memory usage but also requires careful management to avoid errors.

Swapping Array Elements

Swapping elements is a common operation in array manipulation. The exercise provides a straightforward example of swapping the first and last elements of an array. The implementation uses a temporary placeholder to prevent data loss:

int temp = *firstElem;
*firstElem = *lastElem;
*lastElem = temp;

This technique ensures that the value in the first element of the array is not overwritten when the last element's value is assigned to it. The temporary variable 'temp' holds the initial value of 'firstElem' until the swap is complete. After 'lastElem' has been copied over to 'firstElem', the value stored in temp is then assigned to 'lastElem'.

This operation utilizes indirection through pointers, meaning that 'firstElem' and 'lastElem' are not the values themselves but addresses pointing to the values. Thus, when the swapping occurs, it's the values at those specific memory addresses that are exchanged.

Swapping is a building block for more complex algorithms, such as sorting algorithms, and thus mastering this simple operation is foundational for further study in computer science and programming.