Lecture 9: Traverse fixed-size arrays within bounds

## The general form of an array declaration, an index, and a traversal

~~~cpp
#include <array>
std::array<T, <constant size>> <name>{ <value>, ... };  // preferred
T <name>[<constant size>] = { <value>, ... };           // C-style
T <name>[] = { <value>, ... };        // size taken from the list

<name>[<index>]     // 0 <= <index> < <constant size>
<name>.size()       // std::array only
for (std::size_t <i> = 0; <i> < <name>.size(); ++<i>) {
    // use <name>[<i>]
}
for (T <e> : <name>) {
    // use <e>
}
void <fn>(const std::array<T, <constant size>>& <name>);
void <fn>(T <name>[], int <size>);   // C-style: pass the size
~~~

| Part | Meaning |
| --- | --- |
| `<constant size>` | A compile-time constant. The size is fixed for the array's whole lifetime, and for `std::array` it is part of the type. |
| `<index>` | Zero-based, so the last valid index is `<name>.size() - 1`, never `<name>.size()`. |
| counter-controlled `for` | Names each position, so use it when the index itself matters. |
| range-based `for` | Visits every element exactly once, which removes the chance of stating the bound wrongly. |
| C-style array | `int <name>[5] = {1,2,3,4,5};` works and is what C uses, but it has no `.size()` — you must track the size yourself. |
| C-style array parameter | Decays to a pointer at the call, so the function cannot recover the size — pass the size beside it. |

An out-of-bounds index is undefined behavior, not a reported error: the program may print nonsense and keep running.