#!/usr/bin/perl
open(IN, "<data.in") or die ("inFile not found -- $!\n");
open(OUT, ">data.out") or die ("outFile not found -- $!\n");

while(<IN>)
{
    local $/='<tr>';
    my $cnt=0;
    while(/<tc>/){
        s!<tc>!'<tc cNum="'.++$cnt.'">'!ie;
    }
    print OUT;
}

close(IN);
close(OUT);