Notation Conversion Calculator (Infix / Prefix / Postfix)

Enter a standard infix notation expression, and it will convert it to prefix (Polish notation) and postfix (Reverse Polish notation).

You can also convert expressions written in prefix or postfix notation back to infix. The app displays a fully parenthesized form as well, so you can see at a glance "in what order is this expression calculated?" It supports functions like √ and sin, π, variables, negation, exponentiation, and modulo operations, and accepts full-width input too.

The highlight is that you can see the mechanics of calculation visually. The structure of the expression is displayed as a tree diagram, and the traversal order is shown through animation. You'll experience firsthand how the three notations are "different ways of traversing the same tree." Furthermore, you can verify the shunting-yard algorithm, RPN evaluation, and the step-by-step simplification process with stack diagrams, one step at a time.

There's also a learning quiz included. Difficulty comes in three levels, and you can choose from conversion, reverse conversion, or calculation result problems. Dark mode, history, and share links are also available. Feel free to use it for class materials, programming study, or just to kill some time.