0

In this project, I'm trying to create a calculator for simple math and more advanced math such as sin, cos, and the others. While I was writing the code, I ran into a problem with the if statement. The console wrote that:

Exception in thread "main" java.util.NoSuchElementException
        at java.base/java.util.Scanner.throwFor(Scanner.java:937)
        at java.base/java.util.Scanner.next(Scanner.java:1594)
        at java.base/java.util.Scanner.nextDouble(Scanner.java:2564)
        at basiccalculator.main(basiccalculator.java:14)

import java.util.Scanner;

public class basiccalculator {
  public static void main(String[] args) {
    Scanner read = new Scanner(System.in);
    System.out.println("Do you want to use a simple calculator?" + "\n Please, answer with yes / no!");
    String input = read.nextLine();
    read.close();

    if (input.equals("yes")) {

      System.out.println("Enter two numbers: ");
      Scanner scan1 = new Scanner(System.in);
      double first = scan1.nextDouble();
      double second = scan1.nextDouble();

      System.out.print("Enter an operator (+, -, *, /): ");
      char operator = scan1.next().charAt(0);
      double result = 0.0;

      switch (operator) {
      case '+':
        result = first + second;
        break;

      case '-':
        result = first - second;
        break;

      case '*':
        result = first * second;
        break;

      case '/':
        result = first / second;
        break;

      default:
        System.out.println("ERROR");
        break;
      }

      System.out.println(first + " " + operator + " " + second + " = " + result);

      scan1.close();

    } else if (input.equals("no")) {

      Scanner take = new Scanner(System.in);
      System.out.println("Write the degree you want to calculate.");
      double degree = take.nextDouble();
      System.out.print("Enter an operator (sin, cos, tg, cotg): ");
      String angle = take.next();

      switch (angle) {
      case "sin":
        double radians = Math.toRadians(degree);

        double sinValue = Math.sin(radians);

        System.out.println("sin(" + degree + ") = " + sinValue);
        break;

      }
      take.close();

    }

  }
}

The problem I think is the if statement but I may be wrong. I am studying Java on my own, so I expect that there will be a lot of mistakes. If you see some kind of simpler way or something, please tell me.

Mark Rotteveel
  • 100,966
  • 191
  • 140
  • 197
lubo dimoff
  • 41
  • 5
  • Start by 1) get rid of both `scan1` and `take`, 2) just use `read` for all your input; 3) never close `read`. Having multiple `Scanner`s reading from `System.in` is potentially dangerous, especially when you `close` any of them. If switching to a single `Scanner` that you never close doesn't cure the problem, at least now you know it's a legitimate problem. – Kevin Anderson Mar 26 '21 at 09:07
  • The problem is caused by `read.close()`. Never close a scanner wrapping `System.in` because that will also close `System.in`, and use only a single scanner for input, don't repeatedly create new ones. – Mark Rotteveel Mar 26 '21 at 10:29
  • Mr. Rotteveel, thank you very much! The program has finally worked !!! – lubo dimoff Apr 02 '21 at 19:07

0 Answers0