Why does double x = 0,1; not compile?

Question

double x = 0,1;

doesn't compile (tries on on MSVC9.0). The error is

C2059 syntax error : 'constant'

I do realize that there's a comma there instead of a point, but shouldn't the line above be interpreted as the following?

double x = (0,1); //which is double x = 1;

Incidentally, the initialization compiles successfully with the parentheses.

I was thinking along the lines that operator , has a lower precedence than operator =, but in this case = is no operator, so this shouldn't be an issue. What syntactic rules determine that

 double x = 0,1; 

should be illegal?

Answer 1

During declarations, the comma in the absence of parenthesis is treated as a separator between declarations. For example:

double x = 0, y = 1;

or

double x = 0, y;

What you typed is the equivalent of

double x = 0;
double 1; 

Which is obviously not correct.

Answer 2

Well, it's treated as

double x = 0; double 1;

that's why. Just like you'd write

double x = 0, y;

It's the syntax for a declaration, you're just attempting to declare 1 as a variable (which is wrong). Don't think there's much more to it...