What is the function of an array index in C++?

An array index in C++ serves the primary function of accessing specific elements within an array. In C++, arrays are collections of elements that are accessed using an index, which represents the position of an element within the array. The first element of the array is at index 0, the second at index 1, and so on. This numbering system allows programs to retrieve or manipulate data stored in the array efficiently.

For example, if you have an array of integers named arr, you can access the first element using arr[0], the second element using arr[1], and so forth. This indexing mechanism is crucial for reading and writing data to specific locations in the array, enabling effective data management in programming.

The other choices reflect different concepts related to arrays in C++. Modifying the content of an array is a broader operation that can be achieved using an index, but the index's specific role is not to modify but to access. Declaring an array involves specifying its type and size, separate from how elements of the array are accessed. Storing multiple data types is not applicable to standard arrays in C++ since arrays are intended to hold elements of the same data type only.