Between the previous and the next sequence point an object shall have its stored value modified at most once by the evaluation of an expression.Consider line A. The full expression (the assignment to x) assigns two values (1 and 2) to g. Each such assignment is surrounded by sequence points. However, there is no sequence point between the two operands of the addition, and therefore no defined order of evaluation of the two inner assignments. There are a number of possible interpretations of the C Standard that can be made.
In this interpretation, the expression is clearly undefined, because the two assignments to g may take place simultaneously and interfere destructively with one another. However, if this model is applied to line B, it yields the same result (since the sequence points occur at the same places). This means that, in effect, two function calls can be taking place simultaneously, and, if they modify the same object, the effect is undefined. This would surprise many users of the C Standard.
In line A, there are five atomic sequences:(i) evaluate 10