a style question

[Jeffrey T. Hutzelman]

steve at taumet.com (Stephen Clamage) writes:

> aryeh at cash.uucp (the over worked C something or another) writes:
>
>>Since I going to be doing my first team effort I want to know if this
is
>> bad style:
>>	for(x=0;x!=100;x++) ...
>
> In his book "C Traps and Pitfalls", Andy Koenig recommends using
> asymmetric bounds.  In this particular example, there are 101
> iterations, while the casual reader might read it as 100.  If you write
> instead

In this case, the "casual reader" would be correct.  There ARE 100
iterations: x==0 to x==99.

>	for(x=0; x < 101; x++) ...

NO!  That would add the iteration for x==100, which is clearly NOT what
is wanted if he wrote x!=100.  You mean

for(x=0; x < 100; x++) ...

which would cause the same number of iterations as the original loop.

> where the lower bound is INclusive and the upper bound is
> EXclusive, it makes it very obvious what is going on.  Furthermore,
> such loops are often used to address arrays.  Writing the bounds this
> way nicely parallels the array declaration
>	T ray[101];
> where ray has 101 elements from 0 up to but not including 101.  The
> result tends to be fewer off-by-one errors, and code which is easier to
> understand.

Agreed, but again, you mean T ray[100]; which has 100 elements from
0 to 99.

>
> Finally, a test like x!=100 implies that x==101 means continue; it
> requires careful study of the code to see whether x could ever be 101
> or greater.

This is correct.  Good point.

> When you write x<101 it is perfectly plain that x is always
> intended to to less than 101.

Change to "x<100" and "less than 100", which is what was originally
meant.

> -- 
>
> Steve Clamage, TauMetric Corp, steve at taumet.com

I hope this didn't sound too much like a flame, but I wanted to make
sure the record was kept straight.
-----------------
Jeffrey Hutzelman
America Online: JeffreyH11
Internet/BITNET:jh4o+ at andrew.cmu.edu, jhutz at drycas.club.cc.cmu.edu

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