calc PI

https://en.wikipedia.org/wiki/Pi

code

https://github.com/HHS-IntroProgramming/Calculate-Pi

https://github.com/morphx666/CalcPi

https://github.com/Drethic/eve-pi-calc

https://github.com/SaltyPaws/calculator_pi

https://github.com/nohal/Calc_pi_muparser

https://github.com/coq-contribs/pi-calc