text: If there are only three characters , middle one must be operator and corner ones must be operand
code: if ( $ low == ( $ high - 2 ) ) { $ num = eval1 ( ord ( $ expr [ $ low ] ) - ord ( '0' ) , $ expr [ $ low + 1 ] , ord ( $ expr [ $ low + 2 ] ) - ord ( '0' ) ) ; array_push ( $ res , $ num ) ; return $ res ; }