$mn is an array and i don't see where you are incrementing to the next element in the array.
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nevermind i see it now
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wait,...
if @monthno was 1 meaning January, with $mn[1-1] that would be $mn[0] and in your array that would be the first element in the array '0' not January as it should be.
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Edited by Benny69 (2007-02-21 04:37 PM)
