Nobody has mentioned that scanf has undefined behavior on numeric overflow. If INT_MAX is 2147483647 and the user enters 2147483648, the behavior is undefined.

Nobody has mentioned that scanf has undefined behavior on numeric overflow. If INT_MAX is 2147483647 and the user enters 2147483648, the behavior is undefined. (That doesn't just mean you can get an arbitrary value for a and/or b. It means that the standard says nothing at all about how the program behaves). Reference: N1570 (C11) 7.21.6.2 paragraph 10: "If this object does not have an appropriate type, or if the result of the conversion cannot be represented in the object, the behavior is undefined." strtol() avoids this problem.