Chapter 11:

1. Undefined behavior is what happens when a program is executed out of contract: the specification says what the valid inputs are and what the results should be. If invalid input is detected, this is also a part of the contract. If the invalid input is not detected and the program proceeds on the (false) assumption that the input is valid, the results are undefined: the specification does not say what must happen.
2. In C++, there are two main reasons for allowing undefined behavior. First of all, there are operations that require hardware support or are executed differently on different hardware. It may be very difficult or even impossible to deliver a specific result on some hardware systems. The second reason is performance: it may be expensive to guarantee a specific outcome across all computing architectures.
3. No, an undefined result does not mean that the result must be wrong. The desired result is also permitted under undefined behavior, it's just not...