Subject:
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Re: A structured programming question
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 18 Mar 2005 21:21:01 GMT
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Viewed:
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1073 times
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in lugnet.robotics Mr S wrote:
> if $value is not numeric
> then ... do something
> else if $value is numeric and > 40 and < 65
> then ... do something different
> end if
> Both of the latter examples test for a negative result
> prior to setting the action test. My question is this.
> How correct is it to do this, test for negative
> returns prior to acting on a positive return in the
> test, when it is known that $value can be any possible
> value.
What i can tell you is that you should have a more formal workout,
of what an algorithm is.
What is wrong with your algorithm design is the logic. What you call
a negative result is redundant in the above example. You could write
your example like that:
if $value is not numeric
then ... do something
else if $value > 40 and < 65
then ... do something different
end if
implying, that if the second condition isnt true, nothing happens.
Because if its not numeric, then you know that and do not need to
test it again.
There are different programming languages underway. Some distinguish
between data types, some do not.
Examples of scalar data types: boolean, integer, float, string
If you got a given variable content and ask yourself, what datatype
the content is of, you are in two situations: if your programming
language does not support datatypes, like for example perl does, you
need to test the content. It is usual to do this with regular
expressions.
If your programming language supports datatypes, you cannot attempt
to identify the datatype from a value you have read.
Because datatyping is strong in those cases. You must know the
datatype, before you read the value.
In perl for example exists a function "ref(variable)" that allows
you to distinguish between scalar variables, arrays and so on.
In case of RCX datalogs you will receive integers only.
Greetings
Ralph
P.S. i would text layout it like that (most popular form today):
if $value is not numeric then
... do something
else
/** note, the value is numeric now **/
if $value > 40 and < 65 then
... do something different
else
... do nothing
endif
endif
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