A RPN calculator program computes expressions written in RPN (Reverse Polish Notation). A RPN expression (or a postfix expression) is one of the following:
- a number X, in which case the value of the expression is that of X;
- a sequence of the form E1 E2 O, where E1 and E2 are postfix expressions and O is an arithmetic operation; in this case, the value of the expression is that of E1 O E2
The following are RPN expressions: