2020.8.11第三十六天

例3.1 求一元二次方程的根

import java.util.Scanner;
public class cjava {
    public static void main(String[] args) {
        float a,b,c,x1,x2;
        Scanner s=new Scanner(System.in);
        System.out.println("输入a,b,c的值:");
        a=s.nextInt();
        b=s.nextInt();
        c=s.nextInt();
        x1=(float)((-b+Math.sqrt(b*b-4*a*c))/(2*a));
        x2=(float)((-b-Math.sqrt(b*b-4*a*c))/(2*a));
        System.out.println("x1="+x1);
        System.out.println("x2="+x2);
    }
}

 例3.2求三角形面积

import java.util.Scanner;
import java.lang.*;
public class cjava {
    public static void main(String[] args) {
        float a,b,c,x1,x2;
        double s,area;
        Scanner g=new Scanner(System.in);
        System.out.println("输入a,b,c的值:");
        a=g.nextInt();
        b=g.nextInt();
        c=g.nextInt();
        if(a+b>c&&b+c>a&&a+c>b)
        {
        s=(a+b+c)/2;
        area=Math.sqrt(s*(s-a)*(s-b)*(s-c));
        System.out.println("area="+area);
        }
        else
            System.out.println("it is not a trilateral!");
    }
}

 例3.3判断字符大小写，大写转换为小写，小写不转换

import java.util.Scanner;
public class cjava {
    public static void main(String[] args) {
        char ch;
        Scanner g=new Scanner(System.in);
        System.out.println("输入ch:");
        String s;
        s=g.next();
        ch=s.charAt(0);
        if(ch>='A'&&ch<='Z')
        {
        ch+=32;
        System.out.println(ch);
        }
        else
            System.out.println(ch);
    }
}

 2.今天不知道怎么用数学函数，百度查询到java.lang

3明天继续写例题