root.java

一个一元二次方程的求根程序,判断根的性质.

import java.lang.*;
import java.io.*; 
public class Root{ 
public static void main(String args[]) throws IOException 
{ 
double A,B,C,x1,x2,x,disc;
String str="i";
BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); 
while(true){
try{
 	System.out.print("please input A:");
 	A=Double.parseDouble(br.readLine());
 	System.out.print("please input B:");
 	B=Double.parseDouble(br.readLine());
 	System.out.print("please input C:");
 C=Double.parseDouble(br.readLine());
 disc=B*B-4*A*C;
 while(A==0&&B==0){
	 	System.out.println("exit");
         	System.exit(0);
 	}
 	if(A!=0&&disc==0){
		x1=-B/2/A;
		x2=-B/2/A;
		System.out.println("have two equle roots:");
		System.out.println("x1="+x1);
		System.out.println("x2="+x2);
        	System.out.println();
 }
 else if(A!=0&&disc>0){
	 	x1=(-B+Math.sqrt(B*B-A*A*C))/2/A;
	 	x2=(-B-Math.sqrt(B*B-A*A*C))/2/A;
	 	System.out.println("have two different roots: ");
	 	System.out.println("x1="+x1);
	 	System.out.println("x2="+x2);
        	 System.out.println();
 }
 	else if(B==0&&A*C<0){
	 	x1=-Math.sqrt(-C/A);
	 	x2=Math.sqrt(-C/A);
		System.out.println("该方程有两个大小相等且相反的根：");
		System.out.println("x1="+x1);
		System.out.println("x2="+x2);
        System.out.println();
 	}
 	else if(A==0&&B!=0){
	 	x=-C/B;
	 	System.out.println("have one root:");
	 	System.out.println("x="+x);
        	 System.out.println();
 	}
 	else if(A!=0&&disc<0){
	 	double M,N;
 	M=-B/2/A;
 	N=Math.sqrt(-(B*B-4*A*C))/2/A;
 	System.out.println("该方程只有虚数根：");
 	System.out.println("x1="+M+"+"+N+"i");
 	System.out.println("x2="+M+"-"+N+"i");
 	System.out.println();
 	}
}
catch(NumberFormatException e)
{
  	 System.out.println("输入有误，请输入数字！");
   	 System.out.println();
}
catch(Exception e)
{ 
  		System.out.println(" "); 
} 
}
}
}