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Reverse Polish notation – Wikipedia, the free encyclopedia

[edit] The RPN algorithm

Generalizing the above example, we can easily describe a method to evaluate any RPN expression:

* While there are input tokens left o Read the next token from input. o If the token is a number Push it onto the stack. o Otherwise, the token is a function. (Operators, like , are simply functions taking two arguments.) It is known that the function takes n arguments. So, pop the top n values from the stack. # If there are fewer than n values on the stack * (Error) The user has not input sufficient values in the expression. Evaluate the function, with the values as arguments. Push the returned results, if any, back onto the stack. * If there is only one value in the stack o The value is the result of the calculation. * If there are more values in the stack o (Error) The user input too many values.