a style question

[Richard Harter]

In article <1990Sep30.050655.13212 at zoo.toronto.edu>, henry at zoo.toronto.edu (Henry Spencer) writes:
> In article <7341 at darkstar.ucsc.edu> 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++) ...

> Most people find it more readable with a bit of space and the statement
> on the next line:

> 	for (x = 0; x != 100; x++)
> 		...

> The cautious would also recommend `x <= 100', but in this situation that
> is arguable.

> I assume `x' is an integer variable, not floating-point.

The original construction is bad style unless the value of x is being
altered within the loop so that x==100 is the termination condition.  If 
this is the typical loop structure <perform loop body for x = 0 ... 99>
the normal idiom is

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

There is a good reason for using this idiom if you think about it.  In 
C an array of size N has valid indices from 0 through N-1.   Since many
loops reference arrays it is normal for an N times loop to use the same
indexing pattern so that the termination condition for a loop with
increasing indices is index >=N or index<N.

There is a general rule of code writing that the termination conditions
used in loops should match the actual termination condition.  If the
actual condition is x<100 that is what you should use rather than the
weaker condition x!=100.  Note that the proposed text fails if the body
of the loop ever alters the value of x to be greater than 100.

As a further point.  If Henry Spencer, who is an expert, can mistranslate
this construction, you can take it as pragmatic evidence that it is
dubious.  
-- 
Richard Harter, Software Maintenance and Development Systems, Inc.
Net address: jjmhome!smds!rh Phone: 508-369-7398 
US Mail: SMDS Inc., PO Box 555, Concord MA 01742
This sentence no verb.  This sentence short.  This signature done.