>how can u classify as to wat i am askin as undefined??
If you'd like, I can also give you precise details as to what a sequence point is and is not. Or your could take our word for it that the code is undefined.
ISO C Standard Section 6.5, Paragraph 2:
Between the previous and next sequence point an object shall
have its stored value modified at most once by the evaluation of
an expression. Further, the prior value shall be read only to
determine the value to be stored. 70)
This paragraph renders undefined statement expressions such as
i = ++i + 1;
a[i++] = i;
i = i + 1;
a[i] = i;