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

Here are two good expressions that work for most C compilers, yet are ambiguous due to sequence points:

x ^= y ^= x ^= y; // in-place swap of two variables

And also

int i=0;
printf("%d %d %d", ++i, ++i, ++i);  // usually prints out 3 2 1... but not for all compilers!