import java.io.IOException;

import java.util.*;

class Cals{

            int Add(int a, int b){

                        return a + b;

            }

            int Sub(int a, int b){

                        return a - b;

            }

            int Mul(int a, int b){

                        return a * b;

            }

            int Div(int a, int b){

                        int tmp;

                        Scanner objSc = new Scanner(System.in);

                        if(b==0){

                                    System.out.println("Khong thuc hien duoc phep tinh");

                                    System.out.print("b=");

                                    tmp = objSc.nextInt();

                                    return a/tmp;

                        }

                        else return a/b;

            }

}

public class demo {

            public static void main(String[] args) throws IOException {

                        int a,b;

                        char ch,con;

                        Scanner objSc = new Scanner(System.in);

                        Cals objCals = new Cals();

                        do{

                                    System.out.print("Nhap a:");

                                    a = objSc.nextInt();

                                    System.out.print("Nhap b:");

                                    b = objSc.nextInt();

                                   

                                    System.out.println("Moi ban nhap 1 ky tu (+,-,*,/)");

                    ch = (char)System.in.read();

                   

                    switch(ch)

                    {

                                                case '+':           System.out.println("Tong 2 so: "+objCals.Add(a, b));

                                                                                    break;

                                                case '-': System.out.println("Hieu 2 so: "+objCals.Sub(a, b));

                                                                                    break;

                                                case '*':            System.out.println("Tich 2 so: "+objCals.Mul(a, b));

                                                                                    break;

                                                case '/': System.out.println("Thuong 2 so: "+objCals.Div(a, b));

                                                                                    break;

                                                default:            System.out.println("Nhap sai");break;

                    }

                        System.in.skip(ch);

                                                System.out.println("Tiep tuc khong?(Y/N)");

                                                con = (char)System.in.read();

                        }while(con == 'Y' || con == 'y');

            }

}

Trương Đình Huy