gistfile1.java

import java.util.Scanner;

class Calculator
{
	private double firstNumber = 0;
	private double secondNumber = 0;
	private String operation = null;
	private String expression = null;
	
	public double stepByStep() throws NumberFormatException
	{
		double answer = 0;
		Scanner userScanner = new Scanner(System.in);
		
		System.out.println("Please enter your first number");
		firstNumber = userScanner.nextDouble();

		System.out.println("Please enter your second number");
		secondNumber = userScanner.nextDouble();

		System.out.println("Please enter an operation");
		operation = userScanner.next();

		switch(operation)
		{
		case "+":
			answer = (firstNumber + secondNumber);
			break;
		case "-":
			answer = (firstNumber - secondNumber);
			break;
		case "/":
			answer = (firstNumber / secondNumber);
			break;
		case "*":
			answer = (firstNumber * secondNumber);
			break;
		case "x":
			answer = (firstNumber * secondNumber);
		}
		
		userScanner.close();
		
		return answer;
	}
	
	public double expression() throws NumberFormatException
	{
		double answer = 0;
		Scanner userScanner = new Scanner(System.in);
		
		System.out.println("Please enter your expression");
		expression = userScanner.nextLine();

		if(expression.contains("/"))
		{
			String[] sarr = expression.split("/");
			firstNumber = Integer.parseInt(sarr[0]);
			secondNumber = Integer.parseInt(sarr[1]);
			answer = firstNumber / secondNumber;
		}
		else if(expression.contains("-"))
		{
			String[] sarr = expression.split("-");
			firstNumber = Integer.parseInt(sarr[0]);
			secondNumber = Integer.parseInt(sarr[1]);
			answer = firstNumber - secondNumber;
		}
		else if(expression.contains("*"))
		{
			String[] sarr = expression.split("\\*");
			firstNumber = Integer.parseInt(sarr[0]);
			secondNumber = Integer.parseInt(sarr[1]);
			answer = firstNumber * secondNumber;
		}
		else if(expression.contains("+"))
		{
			String[] sarr = expression.split("\\+");
			firstNumber = Integer.parseInt(sarr[0]);
			secondNumber = Integer.parseInt(sarr[1]);
			answer = firstNumber + secondNumber;
		}
		
		userScanner.close();
		
		return answer;
	}
	
	public static void main(String[] args)
	{
		try
		{
			System.out.println("Hello what would you like to do?");
			System.out.println("1)Use basic calculator (Step by step)");
			System.out.println("2)Use basic calculator (Enter an expression)");
			
			int userChoice;
			double answer = 0;
			Scanner userScanner = new Scanner(System.in);
			userChoice = userScanner.nextInt();
			
			Calculator calc = new Calculator();

			if(userChoice == 1)
			{
				answer = calc.stepByStep();
			}
			else if(userChoice == 2)
			{
				answer = calc.expression();
			}
			
			userScanner.close();
			System.out.println("Answer is " + answer);
		}
		catch(NumberFormatException e)
		{
			System.out.println("That is not valid, please restart and enter something valid.");
			System.exit(0);
		}
	}
}