xslt counter value in a variable

I need to iterate through the xml file and store the value of the node number where a particular string is matched.Later i will use this number somewhere else in the xslt.How do i do it.
Code pasted below explains it better.

<row>
<cell>A<c/cell>
<cell>B<c/cell>
<cell>C<c/cell>
<cell>D<c/cell>
<cell>E<c/cell>
<cell>F<c/cell>
<cell>G<c/cell>
</row>

Suppose i want to match string "C".
Then in the above case the value of the variable should be 3.Start Free Trial