Why are types always a certain size no matter its value?

Question

Implementations might differ between the actual sizes of types, but on most, types like unsigned int and float are always 4 bytes. But why does a type always occupy a certai

Answer 1

Because it would be very complicated and computation heavy to have simple types with dynamic sizes. I'm not sure it this would be even possible.
Computer would have to check how many bits the number takes after every change of its value. It would be quite a lot additional operations. And it would be much harder to perform calculations when you don't know sizes of variables during the compilation.

To support dynamic sizes of variables, computer would actually have to remember how many bytes a variable has right now which ... would require additional memory to store that information. And this information would have to be analyzed before every operation on the variable to choose the right processor instruction.

To better understands how computer works and why variables has constant sizes, learn basics of assembler language.

Although, I suppose it would be possible to achieve something like that with constexpr values. However, this would make the code less predictable for a programmer. I suppose that some compiler optimizations may do something like that but they hide it from a programmer to keep things simple.

I described here only the problems that concerns performance of a program. I omitted all problems that would have to be solved to save memory by reducing sizes of variables. Honestly, I don't think that it is even possible.

---

In conclusion, using smaller variables than declared has sense only if their values are known during the compilation. It is quite probable that modern compilers do that. In other cases it would cause too many hard or even unsolvable problems.