Why is this vector out of bounds?

Question

Please explain
https://code.sololearn.com/cbsOBpT5I4kv/?ref=app

Answer 1

On line 13 - 14:
for (int i = 0; i <= SIZE; i++)
a.at(i) = 8;

You should use < not <=

If you try to access elements at index < 0 or index >= a.size() at method throws std::out_of_range exception

Answer 2

Problem's here:

for (int i = 0; i <= SIZE; i++)

Because you use <=, you also ask for a[3] which doesn't exist.