// User input validation - for number of x to process
// input: no input, but this method listens to users' keyboard input.
// output: number of x to process, x is an integer bigger than 0.
public static int numberOfXToProcess() {
	String numberOfXString;
	int numberOfX;
	while(true) {
		//	listen to input and save the values
		Scanner keyboard = new Scanner(System.in);
		System.out.println("Please enter the number of x values to process:");
		numberOfXString = keyboard.nextLine();

		try{
			// convert the string to integer
			numberOfX = Integer.parseInt(numberOfXString);
			// return the int if it's bigger than 0; give alert if not
			// your code goes here

		} catch(NumberFormatException nFE) {
			System.out.println("Your input has to be an integer bigger than 0. Try again.");
		}
	}
}