Keeping the threat of undefined behaviour in mind, and taking steps accordingly, rather than complacently ignoring it. C is a highly unsafe language, and the programmer shouldn't forget this.

> any complicated thing that can be easily ignored, inevitably will be.

The demonstrable inability of C programmers to write correct code is a strong argument against the widespread use of C. Even old languages like Ada show that you can use a language much safer than C and still achieve solid performance. Languages like Rust are making further progress on having safety, performance, and programmer-convenience, all at once.

If you use an ultra-safe language like verified SPARK Ada, the language doesn't even allow you to, say, forget to check whether a denominator is zero, or to forget to protect against out-of-bounds array access.

> Must I pepper the code with bounds checks (which are prone to UB too if not done carefully)?

Not necessarily; a tool can help check for undefined behaviour. Static analysers, GCC flags, and tools like Valgrind, can automatically check for out-of-bounds array access, divide-by-zero, or attempting to dereference NULL. [0] Adding your own runtime assertions isn't a crazy idea though, especially for dev builds. If this were the norm in C programming we'd have fewer security vulnerabilities.

C lacks the kind of runtime checks that are 'always on' in languages like Java and C# (out-of-bounds, divide-by-zero, etc). That's not because such checks don't apply to C code, it's because of the minimalist C design philosophy. You have the option to add your own checks, or use tools to do so automatically, but if you develop without any checks anywhere you should expect to have more bugs. Java added them for a reason.

The C++ language has a somewhat different design philosophy, but it's the same reason its std::array class-template has both a runtime-checked at member-function, and an unchecked operator[]. It would be against the design philosophy to force you to pay the runtime overhead for checks, but it gives you the option.

> which are prone to UB too if not done carefully

What kind of error do you have in mind here?

[0] https://stackoverflow.com/a/44820924/