Is the behaviour of if(++i) ++i defined?

Question

Suppose I have this code:

int main(void)
{
    int i = rand();
    if (++i) ++i;
    return i;
}

Is the behaviour defined here? I know that i = ++i is undefined and the second line in main contains a similar thing. The rand() call is there to stop the compiler from optimising out what I think is the offending line.

Answer 1

From C standard

The following are the sequence points described in:-

.... Between the evaluation of a full expression and the next full expression to be evaluated. The following are full expressions: an initializer that is not part of a compound literal (6.7.9); the expression in an expression statement (6.8.3); the controlling expression of a selection statement (if or switch) (6.8.4); the controlling expression of a while or do statement (6.8.5); each of the (optional) expressions of a for statement (6.8.5.3); the (optional) expression in a return statement.

So yes this is valid. I am just showing you the standard quote so that you feel satisfied that rule is stated somewhere.