Should a function have only one return statement?

Answer 1

Single exit point - all other things equal - makes code significantly more readable. But there's a catch: popular construction

resulttype res;
if if if...
return res;

is a fake, "res=" is not much better than "return". It has single return statement, but multiple points where function actually ends.

If you have function with multiple returns (or "res="s), it's often a good idea to break it into several smaller functions with single exit point.