An array is a fixed-size sequence of elements of the same type stored in contiguous memory. The index of an element determines its address: base + index * sizeof(element). This means any element is reachable in O(1) time without traversal, and the memory layout is cache-friendly — iterating over an array touches sequential cache lines rather than chasing pointers.

int a[8] = {10, 20, 30, 40, 50, 60, 70, 80};
 
a[0]  // 10 — first element
a[7]  // 80 — last element
a[8]  // undefined behaviour — out of bounds

Arrays are the foundation of nearly every other data structure. A Stack, Queue, and Circular buffer can all be implemented over a fixed array. A Matrix is a 2D array with an index formula that maps row and column to a flat offset. The trade-off is the fixed size: the capacity must be known at allocation time. When the required size is not known in advance, a Dynamic array grows the backing array as needed.