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How does a static array differ from a dynamic array?

Data StructuresJunior~1 min read
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A static array and a dynamic array differ in how and when memory is allocated to them and whether the array's size can change while the program is running.

1. Static array

  • The size is set once, at creation time.
  • Memory is allocated in advance (on the stack or in a fixed memory area).
  • The number of elements cannot be changed: if more is needed, a new array must be created.

Example (C):

c
int a[5]; // an array of 5 elements

If a 6th element is needed, it's impossible to add one, the array has to be recreated.

Pros:

  • Simple structure.
  • Fast access to elements.
  • No memory reallocations.

Cons:

  • The size cannot be changed.
  • Extra memory may be wasted if allocated "with a margin".

2. Dynamic array

  • The size can be changed at runtime.
  • Memory is allocated on the heap as needed.
  • On overflow, a new memory block is created and the elements are copied there.

Example (Python / C++):

python
arr = [1, 2, 3] arr.append(4) # adding a new element

(In C++ it's std::vector, in Java it's ArrayList.)

Pros:

  • Flexibility: you can add and remove elements.
  • The size grows automatically.

Cons:

  • Sometimes all elements get copied during expansion (expensive in time).
  • Less predictable memory usage.

3. Visually

Static:

javascript
[ ][ ][ ][ ][ ] ← fixed size

Dynamic:

javascript
[ ][ ][ ] → (overflowed) → creates [ ][ ][ ][ ][ ][ ] and copies

Summary:

A static array is fixed in size, fast and simple. A dynamic array is resizable and flexible, but sometimes spends time on memory reallocation.

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