XSLT: Version 1.0

Requriement: Converting xml to xml files.

XSL file:

<xsl:attribute name="nb-discount">
	<xsl:variable name="d" select="Charge[@Id='99']/@Amount -
Charge[@Id='125']/@Amount"/>
	<xsl:if test="$d">
		<xsl:value-of select="$d"/> <!-- Output is
nb-discount="" why the output is not 0 as expected-->
	</xsl:if>
</xsl:attribute>

XML file:

1) <Charge Id="99" Amount="12.60" CurrCode="EUR" Type="9" PT="P"/>
   <Charge Id="125" Amount="12.60" CurrCode="EUR" Type="5" PT="P"/>
   Actual Output: nb-discount=""
   Expected Output: nb-discount="0"

2) <Charge Id="99" Amount="12.60" CurrCode="EUR" Type="9" PT="P"/>
   <Charge Id="125" Amount="14.60" CurrCode="EUR" Type="5" PT="P"/>
   Actual Output: nb-discount="-2"
   Expected Output: nb-discount="-2"


Regards,
Raja