In order for the user to enter a floating point number, try using the functions in the java.lang.Double class with the following signatures:

public static Double valueOf( String s);

and

public double doubleValue();

For example:

BufferedReader stdin = new BufferedReader(new InputStreamReader (System.in));
String usersInput = stdin.readLine();
Double theNumberAsAnObject = Double.valueOf( usersInput);
double theValue = theNumberAsAnObject.doubleValue();

In other notes you should make sure you use curly braces around the code you want executed inside an if statement. Also, in order to catch out of bounds values from a user, you probably want to ask for the input inside a loop. There's an example or two in the book, but the general idea is this (in pseudo-code):

boolean answerIsInBounds = false;
double theanswer = -1;  // This need to be declared outside the while loop!!!!
while( !answerIsInBounds) {
	printThePrompt();
	theanswer = usersInput();
	if(( theanswer > 0) && (theanswer < 100)) {   // bounds of 0 to 100
		answerIsInBounds = true;
	}
}
// Use the answer here.