In which versions of the C++ standard does “(i+=10)+=10” have undefined behaviour?

Question

In C++, does the following have undefined behaviour:

int i = 0;
(i+=10)+=10;

There was some debate about this in the comments to my answer

Answer 1

In C++11 the expression is well defined and will result in i == 20.

From [expr.ass]/1:

In all cases, the assignment is sequenced after the value computation of the right and left operands, and before the value computation of the assignment expression.

This means that the assignment i+=1 is sequenced before the value computation of the left hand side of (i+=10)+=10, which is in turn sequenced before the final assignment to i.

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In C++03 the expression has undefined behavior, because it causes i to be modified twice with no intervening sequence point.