[alberto-m]

> An alternative view is that any C "unsigned" is both positive and negative. For example the unsigned short "1" is the same number as "65537" and as "-65535".

This can be disproven by the fact that dividing by `unsigned e = 1U` is well defined and always yields the starting number. If the unsigned numbers were really modular numbers as you suggest, division could not be defined.

[adrian_b]

This does not demonstrate anything. It is just additional evidence that the C standard contains contradictory rules about "unsigned" integers.

The oldest parts of the C language are all consistent with "unsigned" numbers being non-negative integers. The implicit conversions between different sizes of "unsigned", the sizeof operator, the relational operators and division are consistent with non-negative integers.

However the first C standard, instead of defining the correct behavior has left undefined many corner cases of the arithmetic operations, allowing the implementation of "unsigned" as either non-negative integers or integer residues.

Eventually, the undefined behaviors for addition, subtraction and multiplication have been defined to be those of integer residues, not those of non-negative integers.

These contradictory properties are the cause of many confusions and bugs.

In extensible languages, like C++, it is possible to define proper non-negative integers and integer residues and bit strings and to always use those types instead of the built-in "unsigned".

In C, it is better to always use signed numbers and avoid unsigned, by casting unsigned to bigger sizes of signed before using such a value.