RPN is definitely easier to implement. I helped someone do that as a student project and while it was minimally complex, there were no edge cases with the operators.
You pay for that by having a stack rather than a small fixed number of variables.
> You pay for that by having a stack rather than a small fixed number of variables.
you can easily add variables to your rpn calculator. For example ">x" pops the top of the stack into the variable x, and "<x" pushes the value of x to the stack.
You can also interpret parentheses as whitespace to enable users to group parts of the computation (but this may become confusing when they write nonsensical parentheses).
My HP RPN calculator only has four positions available in its stack, which I imagine makes the implementation a bit simpler than a stack of arbitrary size.
The typical 4-function calculator doesn't even allow multiple subtrees of computation, so I think it works out to having something like 2 entries on the stack.
You pay for that by having a stack rather than a small fixed number of variables.