2020.8.16第四十一天

例4.7弦截法求方程f(x)=x^3-5x^2+16x-80=0的根

import java.util.Scanner;
import java.lang.*;
public class cjava {
    public static void main(String[] args) {
        double x1,x2,f1,f2,x;
        Scanner a=new Scanner(System.in);
        do
        {
            System.out.println("input x1,x2:");
            x1=a.nextDouble();
            x2=a.nextDouble();
            f1=f(x1);
            f2=f(x2);
        }while(f1*f2>=0);
        x=root(x1,x2);
        System.out.println("A root of equation is "+x);
    }
    static double f(double x) {
        double y;
        y=x*x-5*x+16*x-80;
        return y;
    }
    static double xpoint(double x1,double x2)
    {
        double y;
        y=(x1*f(x2)-x2*f(x1))/(f(x2)-f(x1));
        return y;
    }
    static double root(double x1,double x2)
    {
        double x,y,y1;
        y1=f(x1);
        do
        {
            x=xpoint(x1,x2);
            y=f(x);
        if(y*y1>0)
        {
            y1=y;
            x1=x;
        }
        else
            x2=x;
    }while(Math.sqrt(y)>=0.00001);
        return x;
        }
}

 例4.8递归的方法求n！

import java.util.Scanner;
import java.lang.*;
public class cjava {
    public static void main(String[] args) {
        int n;
        long y;
        Scanner a=new Scanner(System.in);
        System.out.println("please input an integer:");
        n=a.nextInt();
        y=fac(n);
        System.out.println(n+"!="+y);
    }
    static long fac(int n) {
        long f;
        if(n<0)
        {
            System.out.println("n<0,data error!");
            f=-1;
        }
        else if(n==0||n==1) f=1;
        else f=fac(n-1)*n;
        return f;
    }
}

2.遇到的问题：c++中许多的用法java是没有的

3.明天继续写例题