Undefined behavior occurs when C++ imposes no requirements on an operation's result. One example is integer overflow: adding positive int values eventually exceeds the type's representable range, so the language does not define what happens. section 2.3.4
Overflow can appear to wrap around on a particular implementation, but that observed result is not a portable guarantee. Code that depends on it is relying on undefined behavior rather than a language rule. section 2.3.4
Generating too many rows
A row-generation program adds two previous positive numbers and expects every result to remain positive. Eventually, int overflow can produce a negative value or otherwise escape the assumptions of the program. Checking the generated values with std::all_of, std::none_of, or std::ranges::all_of can expose the failure; an assertion can make the expectation explicit. section 2.3.4
Treat undefined behavior as a boundary to test and avoid:
- Do not infer portable behavior from a wraparound result observed in Visual Studio. section 2.3.4
- Check assumptions such as non-negative values while experimenting with generated sequences. section 2.3.4
- Remember that raw pointers, memory-bound violations, and careless low-level operations can also lead to undefined behavior or crashes. section 1.2
