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

To change the size of a variable would require reallocation and this is usually not worth the additional CPU cycles compared to wasting a few more bytes of memory.

Local variables go on a stack which is very fast to manipulate when those variables do not change in size. If you decided you want to expand the size of a variable from 1 byte to 2 bytes then you have to move everything on the stack by one byte to make that space for it. That can potentially cost a lot of CPU cycles depending on how many things need to be moved.

Another way you could do it is by making every variable a pointer to a heap location, but you would waste even more CPU cycles and memory this way, actually. Pointers are 4 bytes (32 bit addressing) or 8 bytes (64 bit addressing), so you are already using 4 or 8 for the pointer, then the actual size of the data on the heap. There is still a cost to reallocation in this case. If you need to reallocate heap data, you could get lucky and have room to expand it inline, but sometimes you have to move it somewhere else on the heap to have the contiguous block of memory of the size you want.

It's always faster to decide how much memory to use beforehand. If you can avoid dynamic sizing you gain performance. Wasting memory is usually worth the performance gain. That's why computers have tons of memory. :)