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import java.util.Scanner;

public class IntroductionJava9_9 {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        System.out.println("Choose 1 for reversed, 2 for average and 3 for equation:");
        int choice = Integer.parseInt(sc.nextLine());
        if (choice == 1) {
            System.out.println("Type your number:");
            int number = Integer.parseInt(sc.nextLine());
            System.out.println(reversed(number));
        } else if (choice == 2) {
            System.out.println("Type length of array:");
            int lengthArr = Integer.parseInt(sc.nextLine());
            int[] arr = new int[lengthArr];
            if (lengthArr == 0) {
                System.out.println("NO ELEMENTS IN ARRAY!");
            } else {
                System.out.println("Type elements of array:");
                for (int i = 0; i < arr.length; i++) {
                    arr[i] = Integer.parseInt(sc.nextLine());
                }
                System.out.println(average(arr));
            }
        } else if (choice == 3) {
            System.out.println("Type 'a' and 'b':");
            int a = Integer.parseInt(sc.nextLine());
            if (a == 0) {
                System.out.println("'A' CAN'T BE 0");
            }
            int b = Integer.parseInt(sc.nextLine());
            System.out.println(equation(a, b));
        } else {
            System.out.println("1, 2 OR 3 NOT DETECTED");
        }
    }

    public static int reversed(int a) {
        int reversed = 0;
        while (a != 0) {
            int digit = a % 10;
            reversed = reversed * 10 + digit;
            a /= 10;
        }
        return reversed;

    }

    public static float average(int[] array) {
        float sum = 0;
        float average = 0;
        for (int i = 0; i < array.length; i++) {
            sum = sum + array[i];
            average = sum / array.length;
            ;
        }
        return average;
    }

    public static float equation(float a, float b) {
        return -b / a;
    }
}
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