[fpc-pascal] Why this evaluates on "if" wrong ?

Daniël Mantione daniel.mantione at freepascal.org
Sun Oct 28 19:38:38 CET 2007

Op Sun, 28 Oct 2007, schreef Joao Morais:

> Daniël Mantione wrote:
> > There is a similar issue here. The value "0.4" cannot be stored exactly
> > in a computer, therefore it is rounded.
> > 
> > This behaviour normal and while annoying, it is simply how things work in
> > the digital world, you will have to work around it.
> Or, of course, use a scaled integer type like Currency.

This is indeed a question you should ask, but you should generalize it. In 
mathematics we consider several groups of numbers:

N - Natural numbers
Z - Integer numbers
Q - Rational numbers
R - Real numbers
C - Complex numbers

Subranges of N, Z and Q can be represented exactly in a computer. R and C 
can not, we use the floating point system as approximation. Very often, a 
certain calculation that on the first sight might tempt one to use a real, 
can be performed in N or Q. In such case floating point is overkill and 
thus, you can save yourself a lot of trouble by calculating it in N or Q.


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