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Tech Tip: How to check if a value is a number
PRODUCT: 4D | VERSION: 2003 | PLATFORM: Mac & Win
Published On: March 25, 2004
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Here's a method you can use to check if a text value is actually a number. This is useful if you are parsing a text file containing a variation of character of numerical strings.

  ` checks if all characters are numerical characters

C_TEXT($1;$char)
C_LONGINT($i)
C_BOOLEAN($isChar)

$isChar:=False

For ($i;1;Length($1))
  If ($isChar)
    $i:=Length($1)
  Else
    $char:=Substring($1;$i;1)
    If ((Ascii($char)<48) | (Ascii($char)>57))
     $isChar:=True
    End if
  End if
End for

  ` is it a character string?
$0:=Not($isChar)

Commented by Garry Lee on January 26, 2011 at 11:04 AM
if $char is an alphabet, Ascii($char) function won't return a numeric value. it returns the alphabet instead.