Calculator

//A simple calculator built to deal wih user-input errors.

import java.util.Scanner;
import java.util.regex.Pattern;


public class Exercise1 {
  
	public static void main(String[] args) {

		String newLine = "";
		Pattern p = Pattern.compile(".*[A-Za-z].*");
		
		while (!newLine.equals("0")) {
		Scanner s = new Scanner(System.in);

		System.out.println("Input desired calculation:");
		newLine = s.nextLine();
		String first = "";
		String second = "";
		double ans = 0;

		while (p.matcher(newLine).matches()) {
			System.out.println("Invalid command!");
			newLine = s.nextLine();
		}
		
		if (newLine.equals("0")) {
			break;
		}
		
		if (newLine.contains("*")) {
			first = newLine.substring(0, newLine.indexOf("*"));
			second = newLine.substring(newLine.indexOf("*")+1, newLine.length());
			ans = Double.parseDouble(first) * Double.parseDouble(second);
		
		} else if (newLine.contains("+")) {
			first = newLine.substring(0, newLine.indexOf("+"));
			second = newLine.substring(newLine.indexOf("+")+1, newLine.length());
			ans = Double.parseDouble(first) + Double.parseDouble(second);
			
		} else if (newLine.contains("-")) {
			first = newLine.substring(0, newLine.indexOf("-"));
			second = newLine.substring(newLine.indexOf("-")+1, newLine.length());
			ans = Double.parseDouble(first) - Double.parseDouble(second);
			
		} else if (newLine.contains("/")) {
			first = newLine.substring(0, newLine.indexOf("/"));
			second = newLine.substring(newLine.indexOf("/")+1, newLine.length());
			ans = Double.parseDouble(first) / Double.parseDouble(second);
		}
		System.out.println(ans);
		}
	}
}