import java.util.Scanner;
class couculator
{
    public static void main(String[] args)
    {
        int num;
        Scanner a = new Scanner(System.in);
        System.out.println("请输入第一个数字。");
        a = a.nextInt();
        Scanner b = new Scanner(System.in);
        System.out.println("请输入加减乘除符号。(1 = +,2 = -,3 = *,4 = /.)");
        b = b.nextInt();
        System.out.println("请输入第二个数字。");
        Scanner c = new Scanner(System.in);
        c = c.nextInt();
        switch (b)
        {
        case 1:
            num = a + c;
            break;
        case 2:
            if (a < c)
            {
                num = a - c;
                break;
            }
        case 3:
            num = a * c;
            break;
        case 4:
            if (a > c)
            {
                num = a / c;
                break;
            }
       
        }
        System.out.println(num);
    }
}

import java.util.Scanner;
    class couculator
    {
        public static void main(String[] args)
        {
            int num=0;
            Scanner a = new Scanner(System.in);
            System.out.println("请输入第一个数字。");
            int s = a.nextInt();
           // Scanner b = new Scanner(System.in);//有用吗？
            System.out.println("请输入加减乘除符号。(1 = +,2 = -,3 = *,4 = /.)");
            int d = a.nextInt();
            System.out.println("请输入第二个数字。");
           // Scanner c = new Scanner(System.in);//有用吗？
            int q = a.nextInt();
            a.close();
            switch (d)
            {
            case 1:
                num = s + q;
                break;
            case 2:
                if (s < q)
                {
                    num = s - q;
                    break;
                }
            case 3:
                num = s * q;
                break;
            case 4:
                if (s > q)
                {
                    num = s / q;
                    break;
                }
           
            }
            System.out.println(num);
        }
}

谢谢，有用谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢！！！！