Answer:
The program in Java is as follows:
import java.util.*;
import java.lang.Math;
public class Rooter{
 public static void main(String[] args) {
     Scanner input = new Scanner(System.in);
  int start;
  System.out.print("Start: ");
  start = input.nextInt();
  while(start<=0){
      System.out.print("Number must be positive\nStart: ");
      start = input.nextInt();  }
  while(start>=0){
      System.out.println(Math.sqrt(start));
      start--;  }
 }
}
Explanation:
This declares start as integer
  int start;
This prompts the user for input
  System.out.print("Start: ");
This gets input for start
  start = input.nextInt();
The following is repeated until the user input is valid i.e. positive
<em>  while(start<=0){</em>
<em>      System.out.print("Number must be positive\nStart: ");</em>
<em>      start = input.nextInt();  }</em>
The following while loop prints the square root of each number till 0
<em>  while(start>=0){</em>
<em>      System.out.println(Math.sqrt(start));</em>
<em>      start--;  }</em>