Unsigned versus signed numbers as indexes

Question

Whats the rationale for using signed numbers as indexes in .Net?

In Python, you can index from the end of an array by sending negative numbers, but this is not the case in .Net. It's not easy for .Net to add such a feature later as it could break other code perhaps using special rules (yeah, a bad idea, but I guess it happens) on indexing.

Not that I have ever have needed to index arrays over 2,147,483,647 in size, but I really cannot understand why they choose signed numbers.

Can it be because it's more normal to use signed numbers in code?

Edit: I just found these links:

The perils of unsigned iteration in C/C++

Signed word lengths and indexes

Edit2: Ok, a couple of other good reasons from the thread Matthew Flaschen posted:

• Historical reasons as it's a c-like language
• Interop with c

Answer 1

Unsigned isn't CLS compliant.

Answer 2

It may be to the long tradition of using a value below 0 as an invalid index. Methods like String.IndexOf return -1 if the element is not found. Therefore, the return value must be signed. If index-consumers would require unsigned values, you would have to a) check and b) cast the value to use it. With signed indices, you just need the check.

Answer 3

For simplicity of course. Do you like trouble doing size arithmetic with unsigned ints?