for ($i = 0; $i < @array; $i++) { 
   if (matches($array[$i])) { 
      $found = $array[$i-1]; 
   } 
}
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Ugh. What if $i = 0 at the match? You've just indexed into the end of the array? Either start at 1, or redefine your problem for the unusual case.

Originally posted as a Categorized Answer.