例题：打印正三角形。两层for循环，难点明白行与列的关系

while (true)
            {
                string s = "★";//s代表五角星
                string t = "○";//t代表方格，如果需要只打印正三角形，可用空格键代替
                int a = 1;//声明变量，初始值为1
                Console.Write("请输入行数");
                a = Convert.ToInt32(Console .ReadLine ());
                for (int i = 1; i <= a; i++)
                {
                    for (int x = 1; x <= a - i; x++)
                    {
                        Console.Write(t);//输出空格，
                    }
                    for (int x = 1; x <= 2 * i - 1; x++)
                    {
                        Console.Write(s);
                    
                    }
                    Console.Write(" ");

打印结果