What is std::vector and why is it the default container?
PICTURE THIS: ARRAY IN MEMORY
Index starts at 0. Scan once for max — O(n).
Simple meaning
Vector is a dynamic array: contiguous, O(1) index, amortized push_back.
WHY — STL instead of guessing?
Why interviewers care about STL:
who only read docs from people who shipped.
and tied to C++ work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Vector is a dynamic
array: contiguous, O(1) index, amortized push_back.
- 2Cache friendliness beats list
for most workloads.
- 3I reserve when I
know the size to avoid realloc copies.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Vector is a dynamic array: contiguous, O(1) index, amortized push_back. Cache friendliness beats list for most workloads.