Calculator.java

import java.util.InputMismatchException;
import java.util.Scanner;

public class Calculator {

	public static void main(String[] args) {
		Scanner number = new Scanner(System.in);
		
		try {
		System.out.println("Choose an operation. a = addition, s = subtraction, m = multiplication, d = division: \n");
		char operation = number.next().charAt(0); // read first character of user input

		
		System.out.println("Enter the first number: \n");
		int num1 = number.nextInt();
		
		System.out.println("Enter the second number: \n");
		int num2 = number.nextInt();
		
		
			
			switch (operation) {
				case 'a':
					System.out.println("The sum is: " + (num1 + num2));
					break;
					
				case 's':
					System.out.println("The difference is: " + (num1 - num2));
					break;
					
				case 'm':
					System.out.println("The product is: " + (num1 * num2));
					break;
					
				case 'd':
					if (num2 != 0)
						System.out.println("The quotient is: " + ((double)num1 / num2));
					else
						System.out.println("Error: Cannot perform division by zero.");
					break;
					
				default:
					System.out.println("Invalid operation. Please enter a, s, m, or d.");
			}
		 } catch (InputMismatchException e) {
	            System.out.println("Error: Please enter valid numbers only!");
	        }
			// This tells Java: “I’m finished reading input — free up the resources. This is to prevent resource leaks”
	        number.close();
	    }
}