import java.util.Scanner;

/**

* Demonstrates input validation using if statements.

*/

public class Logarithm {

public static void main(String[] args) {

// prompt for input

Scanner in = new Scanner(System.in);

System.out.print("Enter a number: ");

// check the format

if (!in.hasNextDouble()) {

String word = in.next();

System.err.println(word + " is not a number");

return;

}

// check the range

double x = in.nextDouble();

if (x > 0) {

double y = Math.log(x);

System.out.println("The log is " + y);

} else {

System.out.println("The log is undefined");

}

}

}