Re: pls expand this macro

sathyashrayan wrote:
> /*
> ** PLURALTX.C - How to print proper plurals
> ** public domain - original algorithm by Bob Stout
> */
>
>
> #include <stdio.h>
>
>
> #define plural_text(n) &"s"[(1 == (n))]
>
> #define plural_text2(n) &"es"[(1 == (n))<<1]
>
> int main(void)
> {
> int i;
>
> for (i = 0; i < 10; ++i)
> printf("%d thing%s in %d box%s\n", i, plural_text(i), i,
> plural_text2(i));
> return 0;
>
> }
>
> My questions:
>
> 1) I try to understand the two macros plural_text and plural_text2.
> array subscripting is commutative
> so in the above we could expand the macros as plural_text n[1] = "s" .
> The parenthesis around
> the variable (n) since the macros does not know the type of the variable
> it is acting on. Am I correct?

* the macro doesn't know the type of the variable.
if you expand the macro, it looks like this

case 1 / plural_text(0) : &"s"[0]
...
>
> 2) I don't able to understand the use of & in both of the macros. Does
> it used for the rule "array decays into
> the pointer to it's first element"?

* "&" operand will make the right-side variable's pointer
so it makes the array of string which started from the index value
of the array..

>
> 3) << operator in the macro plural_text2 used to move the string to the
> second one, in the above case
> it is "s". Correct?

* << operator shifts the result of "(1==(n))",
so its last value is only be "0" or "2"
"0" will be the "es"
"2" will be the NULL

so you can see the boxes, or box

>
> Can any one explain both of the macros.
> --
> "combination is the heart of chess"
>
> A.Alekhine
>
> Mail to:
> sathyashrayan AT gmail DOT com
>
>

I'm poor at english.

- Park, Sung-jae
.

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