RPN Calculator

A simple calculator that uses Reverse Polish Notation (RPN), where operators come after the operands. Enter 1 2 + instead of 1 + 2. Use the UP and DOWN buttons to select a digit or operator, then press SELECT/ENTER to insert it. Keys: C – Clear the current input or delete the last entered digit. E – Enter the current input onto the stack. If no number is being entered, it duplicates the top value on the stack. The calculator uses a configurable stack, with a default depth of 4. The top two stack values are displayed on the screen. The app is free and open source. Feel free to open issues, submit PR-s at https://github.com/zeroflag/ciq-rpn-calc. Alpha version.

UI improvements