language agnostic - Default int type: Signed or Unsigned?

Question

When programming in a C-like language should one's "default" integer type be int or uint/unsigned int? By default, I mean when you don't need negative numbers but either one should be easily big enough for the data you're holding. I can think of good arguments for both:

signed: Better-behaved mathematically, less possibility of weird behavior if you try to go below zero in some boundary case you didn't think of, generally avoids odd corner cases better.

unsigned: Provides a little extra assurance against overflow, just in case your assumptions about the values are wrong. Serves as documentation that the value represented by the variable should never be negative.

Answer 1

The Google C++ Style Guide has an interesting opinion on unsigned integers:

(quote follows:)

On Unsigned Integers

Some people, including some textbook authors, recommend using unsigned types to represent numbers that are never negative. This is intended as a form of self-documentation. However, in C, the advantages of such documentation are outweighed by the real bugs it can introduce. Consider:

for (unsigned int i = foo.Length()-1; i >= 0; --i) ...

This code will never terminate! Sometimes gcc will notice this bug and warn you, but often it will not. Equally bad bugs can occur when comparing signed and unsigned variables. Basically, C's type-promotion scheme causes unsigned types to behave differently than one might expect.

So, document that a variable is non-negative using assertions. Don't use an unsigned type.

(end quote)