Editing Sequence point (section)

==Examples of ambiguity==
Consider two [[subroutine|function]]s <code>f()</code> and <code>g()</code>. In C and C++, the <code>+</code> operator is not associated with a sequence point, and therefore in the [[expression (computer science)|expression]] <code>f()+g()</code> it is possible that either <code>f()</code> or <code>g()</code> will be executed first. The comma operator introduces a sequence point, and therefore in the code <code>f(),g()</code> the order of evaluation is defined: first <code>f()</code> is called, and then <code>g()</code> is called.

Sequence points also come into play when the same variable is modified more than once within a single expression. An often-cited example is the [[C (programming language)|C]] expression <code>i=i++</code>, which apparently both assigns <code>i</code> its previous value and increments <code>i</code>. The final value of <code>i</code> is ambiguous, because, depending on the order of expression evaluation, the increment may occur before, after, or interleaved with the assignment. The definition of a particular language might specify one of the possible behaviors or simply say the behavior is [[undefined behavior|undefined]]. In C and C++, evaluating such an expression yields undefined behavior.<ref>Clause 6.5#2 of the [[C99]] specification: "Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be accessed only to determine the value to be stored."</ref> Other languages, such as [[C Sharp (programming language)|C#]], define the [[order of operations|precedence]] of the assignment and increment operator in such a way that the result of the expression <code>i=i++</code> is guaranteed.