Why is a regular expression bad? They're extremely efficient and simple to understand and the right tool for the job. 
if ( defined($x) && length($x) && $x !~ /\D/ && 0 <= $x && $x <= 10 ) 
+{
    # It matches
}

[download]
Of course, if this is homework, be prepared to explain why each of those is important. :-)
My criteria for good software:
  1. Does it work?
  2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

In reply to Re: check if its a number by dragonchild
in thread check if its a number by m.y

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