I Was Bored

package com.company;
import java.util.Scanner;

class Calculator{
    public static double calculateInput(int num1, char expr, int num2){
        double result;
        final double pi = 3.14;
        switch(expr){
            case '+':
                result = num1 + num2;
                return result;
            case '-':
                result = num1 - num2;
                return result;
            case 'x':
            case '*':
                result = num1 * num2;
                return result;
            case ':':
            case '/':
                result = num1 / num2;
                return result;
            case '%':
                result = num1 % num2;
                return result;
            default:
                System.out.println("Invalid Expression");
                return 0;
        }
    }
}

class Variables{
    public static void printVariables(){
        char[] alphabet = new char[]{'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};
        for (int i = 0; i < 26; i++) {
            for (int j = 0; j < 26; j++) {
                for (int k = 0; k < 26; k++) {
                    System.out.print(alphabet[i]);
                    System.out.print(alphabet[j]);
                    System.out.print(alphabet[k]);
                    System.out.print(", ");
                }
            }
        }
    }
}


public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String[] args){
        boolean a;
        String lol;
        System.out.print("Enter a boolean value: ");
        a = sc.nextBoolean();
        if (a){
            System.out.println("It'll give you all variables name. Do you want it?");
            lol = sc.next();
            if(lol.equals("yes") || lol.equals("Yes") || lol.equals("YES")) Variables.printVariables();
            else System.out.println("It won't give you all variables name");
        }
        System.out.println("Enter an expression");
        int numb1 = sc.nextInt();
        char oper;
        do{
            int uio = 0;
            oper = sc.next().charAt(uio);
            ++uio;
        }while('1' == oper || '2' == oper || '3' == oper || '4' == oper || '5' == oper || '6' == oper || '7' == oper || '8' == oper || '9' == oper || '0' == oper);
        int numb2 = sc.nextInt();
        System.out.println(Calculator.calculateInput(numb1, oper, numb2));
    }
}