java语言程序设计 第十版（基础篇）5.23-26

int n = 50000;
		double sum1=0;
		double sum2=0;
		for(int i =1;i<=n;i++) {
			
			sum1 = sum1 + 1.0/i;
		}
		System.out.printf("result 1:%7.15f\n",sum1);
		
		for(int i=n;i>=1;i--) {
			
			sum2 = sum2+ 1.0/i;
		}
		System.out.printf("result 2:%7.15f\n",sum2);
		System.out.printf("The diffrence between two result is:%7.15f",(sum2-sum1));

	double sum = 0;
		double k =1.0;
		for(int i=3;i<=99;i+=2) {
			
			sum +=  k/i;
			k+=2;
		}
		System.out.printf("The  Sequence sum is :%5.8f",sum);

	java.util.Scanner input = new java.util.Scanner(System.in);
		double sum = 0;
		System.out.print("Enter number of n:");
		int n =input.nextInt();
		
		for(int i =1;i<=n;i++) {
			
			if(i%2==0)
				sum+= (-1.0)/(2*i-1);
			else
				sum+=1.0/(2*i-1);
			
		}
		System.out.printf("when  n= %d  PI is :%5.9f\n",n,4*sum);

	java.util.Scanner input = new java.util.Scanner(System.in);
		System.out.print("Enter number of n :");
		int n = input.nextInt();
		double item = 1;
		double e =1.0;
	
		for(int i =1;i<=n-1;i++) {
			
			item = item/i ;
			
			e+=item;
		}
		System.out.printf("The e is : %5.9f",e);