Which issues have you encountered due to sequence points in C and C++?

Question

Below are two common issues resulting in undefined behavior due to the sequence point rules:

a[i] = i++; //has a read and write between sequence points
i = i++;          


        

Answer 1

An example similar to Dario's, which I've also seen people fall into:

printf("%s %s\n", inet_ntoa(&addr1), inet_ntoa(&addr2));

Not only will this either print "addr1 addr1" or "addr2 addr2" (because inet_ntoa returns a pointer to a static buffer overwritten by further calls), but also it is not defined which of these will be the case (because C does not specify order of evaluation in argument lists).