1+1/2+1/3+…+1/n 從右往左更加精確

import java.util.Scanner;
class Main {
  public static void main(String[] args){
    int n = 50_000;
    double sum = 0;
    for(int i = 1; i <= n; i++){//從左往右加
      sum += 1.0 / i;
    }
    System.out.print("The result is: " + sum);

    double sum1 = 0;
    for(int i = n; i > 0; i--){//從右往左加 更加精確
      sum1 += 1.0 / i;
    }
    System.out.print("\nThe result is: " + sum1);
  }
}
 

1/3 + 3/5 + 5/7+…+ 95/97 + 97/99

import java.util.Scanner;
class Main {
  public static void main(String[] args){
    double sum = 0;
    for(int i = 1; i <= 97;i = i+2)
      sum += (double)i / (i + 2);

    System.out.print("The sum is: " + sum);
    
  }
}

PI = 4 * (1-1/3+1/5-1/7+…+1/(2i-1)-1/(2i+1))

顯示當i為10,000 20,000 … 100,000時PI的值

import java.util.Scanner;
class Main {
  public static void main(String[] args){
    double PI = 0;
    double result = 0;
    int n = 10_000;
    System.out.print("i\t\tPI");
    while(n <= 100_000){
      for(int i = 1; i <= n; i = i + 2)
        result += 1.0 / (2 * i -1) - 1.0 / (2 * i + 1);
      
      PI = 4 * result;
      System.out.print("\n" + n + "\t" + PI);
      result = 0;
      n += 10_000;
    }
  }
}