<P> Calculators that utilize reverse Polish notation (RPN), also known as postfix notation, use a stack to enter formulas without the need for parentheses . </P> <P> Some programming languages use precedence levels that conform to the order commonly used in mathematics, though others, such as APL, Smalltalk or Occam, have no operator precedence rules (in APL, evaluation is strictly right to left; in Smalltalk and Occam, it is strictly left to right). </P> <P> In addition, because many operators are not associative, the order within any single level is usually defined by grouping left to right so that 16 / 4 / 4 is interpreted as (16 / 4) / 4 = 1 rather than 16 / (4 / 4) = 16; such operators are perhaps misleadingly referred to as "left associative". Exceptions exist; for example, languages with operators corresponding to the cons operation on lists usually make them group right to left ("right associative"), e.g. in Haskell, 1: 2: 3: 4: () = = 1: (2: (3: (4: ()))) = = (1, 2, 3, 4). </P> <P> The logical bitwise operators in C (and all programming languages that borrow precedence rules from C, for example, C++, Perl and PHP) have a precedence level that the creator of the C language considered unsatisfactory . However, many programmers have become accustomed to this order . The relative precedence levels of operators found in many C - style languages are as follows: </P>

When does the order of operations not apply