What are off by one errors? How common are they? Are they avoidable?

What will be an ideal response?

Off-by-one errors happen when code is correct except that the beginning or ending index of computation is one more or one less than the correct solution. They happen very frequently since the beginning or end of a sequential computation is a special case that is often difficult to see even when the general solution is clear. They can be avoided through testing and a rigorous consideration of the correct endpoints of a loop process.