import java.util.Scanner;

public class PiApproximator {


   public static int userInput ( String userInput , Scanner scnr ) {

      int userNum;

      userNum = 0;

      while (userNum <= 0) {
         System.out.println(userInput);
         userNum = scnr.nextInt();

         if (userNum <=0) {
            System.out.println("Invalid number. Please enter a non-negative.");
         }
      }
      return userNum;
   }
   public static double piCalcDisplay (int termNum , int dispNum) {
      double pi = 0.0;
      double piNom = 4.0;
      double piDeNom = 1.0;
      dispNum = 1;

      System.out.println("\nRESULTS");

      for (int i = 1; i <= termNum;) {
         if (i % 2 != 0) {
            pi = pi + (piNom/piDeNom);
         }
         else {
            pi = pi - (piNom/piDeNom);
         }
         piDeNom = piDeNom + 1.0;

         i = dispNum * i;

         int termStep = (i * (termNum / dispNum)) / termNum ;

      System.out.printf("%1s %2d %1s %.9f \n" , "At term" , termStep ,  ": Pi = " , pi);

      }
      return pi;
   }

   public static void main(String[] args) {
      Scanner scnr = new Scanner(System.in);
      String userTermPrompt = "Enter number of terms to use";
      String userDispPrompt = "Display Pi after every how many steps?";
      int termNum = 0;
      int dispNum = 0;
      double piResults;





      System.out.println("Program will approximate Pi");

      termNum = userInput(userTermPrompt , scnr);
      //System.out.println(termNum);
      dispNum = userInput(userDispPrompt , scnr);
      //System.out.println(dispNum);

      piResults  = piCalcDisplay(termNum , dispNum);


      System.out.println(piResults);




   }

}