Associativity and Sequence Points in C

Question

Since the associativity of '?' is from right to left,any 2 consecutive '?' operators must be treated as such,Right?

Now,

int x=-1;
int y=x?x++?x:-1:1;

I expect this to be executed as:

int y = x ? (x++?x:-1) : 1;

Now since its being executed from right to left,when encountering the first '?' in the statement,x's value is 0 and the expression is as

int y= x? 0 : 1;

hence i expected y to be 1,but it shows Zero on my dev-cpp.Where am i wrong?

Answer 1

You have the order of evaluation wrong. In a ? b : c, a is always evaluated first, then either b or c is evaluated.

I've marked up your example so that I can identify subexpressions:

            c
int y=x?x++?x:-1:1;
      a bbbbbbbb

(a) is evaluated, yielding -1, so (b) is evaluated. There, x++ is evaluated, yielding -1 again, so (c) is evaluated. At this point, x is 0.

Or, with more verbose, clearer code, it's as if you said:

int x = -1;
int y;
if (x != 0)
{
    int new_x = x + 1;
    if (x != 0)
    {
        y = new_x;
    }
    else
    {
        y = -1;
    }
}
else
{
    y = 1;
}