What range does for (int i = 1; i <= 100; i++) process?
for (int i = 1; i <= 100; i++)
Only multiples of 3 and 5 between 1 and 100.
Integers from 1 through 99 because <= excludes 100.
<=
Every integer from 0 through 99.
Every integer from 1 through 100, including both endpoints.