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From: pcm@iwarpj.intel.com (Phil C. Miller)
Newsgroups: comp.lang.c
Subject: Re: QuickC
Message-ID: <3770@omepd>
Date: 28 Aug 88 20:45:20 GMT
References: <8808261424.AA11504@ucbvax.Berkeley.EDU>
Sender: news@omepd
Reply-To: pcm@iwarpj.UUCP (Phil C. Miller)
Organization: Intel Corp., Hillsboro
Lines: 49

In article <8808261424.AA11504@ucbvax.Berkeley.EDU> TURGUT@TREARN.BITNET (Turgut Kalfaoglu) writes:

>The other day, I was struggling with QuickC - a very simply problem,
>but really intriguing. Let me know if you can interpret this:

>main()
>{
>   int a,v;
>   a = 2;
>   v = square(a);
>   printf("%d\n",v);
>}

>square(num)
>int num;
>{
>  num = num*num;
>}

>OK? There is no 'return' statement in the function. However, it works!
>I get '4' as an answer. So I thought maybe it was keeping the result
>of the last operation, so I added some dummy lines,

>square(num)
>int num;
>{
>  int dummy;
>  num = num*num;
>  dummy=222;
>}

>but the call STILL works... Can anyone shed some light onto this?
>WHY does it work?
>-turgut

Don't know for sure, but I'll offer a conjecture:

The subprogram calling standard for Microsoft C probably has a register doing
double duty: it holds input arguments (i.e., num) and also holds the function
result (unassigned, but with a residual value set when you assigned a value to
the input argument num.

Another conjecture: if you were using an optimizing compiler, it would see that
the value num was dead (i.e., had no further use in the function square) and 
the assignment to num would disappear, along with the 'magic' function value
assignment.

Phil Miller
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