public Double calc(int n1, String op, int n2) {		
		double num1 = (double)n1;
		double num2 = (double)n2;
		
		if (op.equals("+")) {
			return (num1 + num2);
		} else if (op.equals("-")) {
			return (num1 - num2);
		} else if (op.equals("*")) {
			return (num1 * num2);
		} else if (op.equals("/")) {
			// Note: This does NOT handle division by zero!
			return (num1 / num2);
		} else {
			System.err.println("ERROR: INVALID OPERATOR: " + op);
			return null;
		}
	}