Why do random access iterator's arithmetic operators accept / return int and not size_t?

Question

Since most operations on std::vector require / return size_t - that\'s the type I use for indexing. But now I\'ve enabled all compiler warnings to

Answer 1

It allows for things like it += index; where index can be both positive or negative (according to some logic).

Comparing with the following:

if (some_condition)
    it += index;
else
    it -= index;

Which would be needed if we could only pass unsigned values.