A Level Computer Science OCR Practice Exam

What is reverse Polish notation characterized by?

1. The operator precedes the operands

2. The operands are listed first, followed by the operator

3. An equal sign at the end of the expression

4. Operators are nested within parentheses

The correct answer is: The operands are listed first, followed by the operator

Reverse Polish notation (RPN) is characterized by the arrangement where the operands are listed first, followed by the operator. This notation eliminates the need for parentheses to enforce operator precedence, as the order of operations is clearly defined by the position of the operators and operands. In RPN, for instance, to add two numbers, you would input the numbers first and then the operator. So, to add 3 and 4, you would write "3 4 +". This method allows for a more straightforward evaluation of mathematical expressions, particularly useful in stack-based algorithms and computer programming. The other characteristics mentioned in the options are not applicable to RPN. For example, having the operator precede the operands is typical of prefix notation, not reverse Polish. Additionally, using an equal sign at the end is common in traditional notations but not required in RPN. Lastly, nesting operators within parentheses is a feature of infix notation, where the placement of the operator relies on explicit grouping defined by parentheses.