千位数减百位数不退位 区间代换

法1 区间代换

namespace ConsoleApplication32
{
    class Program
    {
        static void Main(string[] args)
        {
            while (true)
            {
                int x, y,a;
                Random r = new Random();
                x = r.Next(1, 10);//千位数随机1-9
                a = r.Next(2, 10);//a为4位数的百位数
                y = r.Next(1, a);//随机数取不到a，故三位数的百位数永远小于a
                
                    Console.WriteLine((x*1000+a*100) + "-" + (y*100) + "=" +((x*1000+a*100)-(y*100)));
                
                Console.ReadLine();
            }
        }
    }
}

法2

namespace ConsoleApplication32
{
    class Program
    {
        static void Main(string[] args)
        {
            while (true)
            {
                int x, y, n, m, p;
                Random r = new Random();
                x = r.Next(1000, 10000);//可以看成x为两位数，y为个位数，两位数x对10取余为a，y = r.Next(0, a);
                y = r.Next(100, 1000);
                m = y / 100;
                p = x / 1000;
                n = (x - p * 1000) / 100;//保证4为数的百位数大于3位数的百位数
                if (n > m)
                {
                    Console.WriteLine(x + "-" + y + "=" + (x - y));
                }
                Console.ReadLine();
            }
        }
    }