Overflow

If we are detecting if a * 10 will overflow INT_MAX, we compare a with INT_MAX / 10. If a > INT_MAX / 10, it will overflow.

If we are detecting if a * 10 + b will overflow INT_MAX, we use this check: If a > INT_MAX / 10 || (a == INT_MAX / 10 && b > INT_MAX % 10), it will overflow.