SimpleCalculator.java

import java.util.Scanner;

public class SimpleCalculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("--- Simple Java Calculator ---");
        System.out.print("Enter the first number: ");
        double num1 = getValidDouble(scanner);

        System.out.print("Enter an operator (+, -, *, /): ");
        char operator = scanner.next().charAt(0);

        System.out.print("Enter the second number: ");
        double num2 = getValidDouble(scanner);

        double result;

        switch (operator) {
            case '+':
                result = num1 + num2;
                System.out.println("Result: " + num1 + " + " + num2 + " = " + result);
                break;
            case '-':
                result = num1 - num2;
                System.out.println("Result: " + num1 + " - " + num2 + " = " + result);
                break;
            case '*':
                result = num1 * num2;
                System.out.println("Result: " + num1 + " * " + num2 + " = " + result);
                break;
            case '/':
                if (num2 == 0) {
                    System.out.println("Error: Division by zero is not allowed.");
                } else {
                    result = num1 / num2;
                    System.out.println("Result: " + num1 + " / " + num2 + " = " + result);
                }
                break;
            default:
                System.out.println("Error: Invalid operator selected. Please use +, -, *, or /.");
        }

        scanner.close();
    }

    // Helper method to prevent scanner crashes on invalid input
    private static double getValidDouble(Scanner scanner) {
        while (!scanner.hasNextDouble()) {
            System.out.print("Invalid input. Please enter a valid number: ");
            scanner.next(); 
        }
        return scanner.nextDouble();
    }
}