nonportable code or incorrect compilers?

[Jonathan Krueger]

Here's a question of portability and language standards that came up in
a real life program.  According to K&R or ANSI, predict the output of
the following code:

#define	DEFCONST	1.05
main()
{
	int	count = 800;

	printf("count is %d, ", count);
	count *= DEFCONST;
	printf("now %d\n", count);
}

My prediction, based on K&R, was the output:
	count is 800, now 839
Indeed, the Pyramid 98x produces exactly this output.
But your mileage may vary.  4.2BSD VAX, Gould, and Sun-3 produce output:
	count is 800, now 800
Which brings me to the question: is this code non-portable, or do
three out of four compilers surveyed fail to correctly implement K&R?

The relevant K&R references appear to be 2.10, Assignment Operators
and Expresssions:
	"If e1 and e2 are expressions, then
		e1 op= e2
	 is equivalent to
		e1 = (e1) op (e2)
	 except that e1 is computed only once."
and 2.7, Type Conversions:
	"float is converted to double, then if either operand is
	 double, the other is converted to double, and the result
	 is double"

Putting it all together, does "e1 is computed only once" imply lack of
ordinary automatic type conversion for e1 and expressions of which it
is a part?  Or does "computed" mean "value derived for", and K&R
in no way implies different type handling from the unabbreviated
expression?  And does ANSI clear up this ambiguity?

-- Jon Krueger