Simple fwrite question

I am trying to have a counter in a file. With what I have below I get in the $counterfile 0 + 01 = 01 01 + 01 = 012 012 + 01 = 01213 [snip] /* Add "1" to the counter */ $counter = ($counter + '01'); /* Verify counter file is writable */ if (is_writable($counterfile)); /* { */ if (!$handle = fopen($counterfile, 'a')) { print "Cannot open file ($counterfile)"; exit; } /* Write to our counter file. */ if (!fwrite($handle, $counter)) { print "Cannot write to file ($counterfile)"; exit; } fclose($handle); [/snip] How do I overwrite the existing value with my new value instead of it adding on after the past values? My other dilemma is, this counter decides what line to display in a sequence from a separate file what command can I use to tell it when $counter is @ the last line in my "tips" file to reset to zero thanks Matt