unsigned

There is another reason: loop index code written to work properly for unsigned will work for signed, but the reverse is not true.

This means you have to think about every loop if you intend to do some kind of global conversion to unsigned.

If you underflow an unsigned you get a huge value that's going to be invalid by any range check unless you assume entire unsigned range is available.

The problem with unsigned integers is that most people, past me included, think that it prevents nonsense negative values.

It makes sense to use unsigned for sizes to save a bit (or 32 bits per size).

If your domain is 0..99 for example, using unsigned and <100 is nicer than using signed and two conditionals.

It might be pretty safe if you're only ever adding, multiplying or dividing with other unsigned numbers.

It just that API have been extended to provide operations that treat an int or a long as having unsigned value.

This causes unsigned arithmetic to contaminate parts of your code that you thought were signed.

That sounds completely wrong, unless the function takes a reference to the unsigned int.

Even worse are mixtures of signed and unsigned operands in expressions; luckily, C compilers tend to have reasonably decent warnings about that.

In fact, prior to Java 8, you could not even declare unsigned integers.

My general rule of thumb is "use unsigned integers when interfacing with hardware, otherwise use int.".

Consequently the answer is "signed unless you have a good reason to need unsigned", because at least then you are more likely to be able to detect an error condition.

Unsigned integers have a big "cliff" immediately to the left of zero.

I nearly left it "unsigned", but my OCD kicked in.

Unsigned overflow is defined but that doesn't necessarily make it any more expected when it happens.