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

It can be less. Consider the function:

int foo()
{
    int bar = 1;
    int baz = 42;
    return bar+baz;
}

it compiles to assembly code (g++, x64, details stripped)

$43, %eax
ret

Here, bar and baz end up using zero bytes to represent.