size vs capacity of a vector?

Question

I am a bit confused about this both of these look same to me. Although it may happen that capacity and size may differ on different compilers. how it may differ. Its also sa

Answer 1

size() tells you how many elements you currently have. capacity() tells you how large the size can get before the vector needs to reallocate memory for itself.

Capacity is always greater than or equal to size. You cannot index beyond element # size()-1.