What is the main difference?
The key idea
An array stores elements contiguously and supports direct indexing. A linked list connects nodes through links, so reaching a position generally requires traversal. This affects access, updates and memory overhead.
An ordinary fixed array has a fixed extent. A dynamic-array container such as a C++ vector adds resizing behaviour, but resizing may require allocating new storage and moving elements. Keep those cases distinct when comparing costs.
Compare the complete operation
| Operation | Array or dynamic array | Singly linked list |
|---|---|---|
| Read element by index | Constant-time indexed access | Linear traversal in general |
| Find an arbitrary value | Linear without another index or ordering advantage | Linear in general |
| Insert at the front | Usually shift existing elements | Update links in constant time with the head known |
| Insert after a known node | Shift elements in the usual array model | Link change can be constant time |
“Known node” is an important qualification. Finding that node may take linear time. A claim that linked-list insertion is always constant time leaves out part of the task.
Work through an insertion
Start with the sequence 10, 20, 30. Insert 15 after 10. In a simple array representation with available capacity, 20 and 30 move right before 15 occupies the new position.
In a singly linked list, once the node containing 10 is known, the new node links to 20 and the 10 node links to the new node. The sequence becomes 10, 15, 20, 30.
If the request only says “insert after the value 10,” you must also consider the search and decide what happens if the value is absent or repeated.
Remember memory and locality
Linked-list nodes need storage for links, and separately allocated nodes may be scattered in memory. Contiguous arrays often offer useful locality when scanning. Actual performance also depends on allocation, element size, hardware and the workload.
Do not select a structure from one complexity label alone. A small array can be a clear, effective choice even when a linked structure appears attractive for one operation.
Test boundary cases on paper
Draw an empty list, a one-node list and a three-node list. Show insertion at the beginning and removal of the first node. Check how the head changes and whether any link is lost.
For an array exercise, state the current element count and available capacity separately. A free storage slot is not automatically an element that belongs to the logical sequence.
Decide from the workload
Choose an indexed structure when frequent position access is central. Investigate linked structures when their update pattern and representation suit the task, while including the cost of obtaining the position.
In Gammal Tech's route, study these comparisons in Data Structures after C++. Your strongest answer is a justified choice with assumptions, not “arrays are better” or “linked lists are faster” in every situation.
References and course details
Use these references for further study. The examples and exercises in this article are educational; consult the catalogue for course details.