Linked list has no random access

In a linked list the nodes are scattered in memory, and the only way to reach a node is through the pointer stored in the node before it. There is no formula like address = base + i × size as in an array. To get the k-th node we must start at start and follow next k-1 times, so access takes O(k) time (O(n) worst case); an array gives A[k] in O(1).

Example: list start -> [10] -> [20] -> [30] -> [40]. To read the 4th element, we visit 10, 20, 30 and only then reach 40; we cannot jump directly to 40.

p = start;
for (i = 1; i < 4; i++) p = p->next;   /* 3 steps */
printf("%d", p->info);                  /* 40 */

Hence data in a linked list cannot be accessed randomly, only sequentially.