public class mySqrt{
	public static void main(String[] arg){
		double y; 
		y=mySqrt(4.); 
		System.out.println("sqrt(4)="+y);
		y=mySqrt(-4);
		System.out.println("sqrt(-4)="+y);
	}
	public static double mySqrt(double a){
		double x; 
		if(a>=0.) {
			x=Math.sqrt(a);
			System.out.println("x="+x);
		}
		else {
			x=Double.NaN;
			System.out.println("error");
		}
		return x; 
	}
}
/*

V:\my teaching.sync\2007.ph265.winter>javac mySqrt.java

V:\my teaching.sync\2007.ph265.winter>java mySqrt
x=2.0
sqrt(4)=2.0
error
sqrt(-4)=NaN

V:\my teaching.sync\2007.ph265.winter>
*/