using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Forxunhuan
{
    class Program
    {
        static void Main(string[] args)
        {
            //上三角
            //I 为乘法的第一个数
            for (int i = 1; i <= 9; i++)
            {
                //j为乘法的第二个数
                for (int j = 1; j <= i; j++)
                {
                    Console.Write("{0}*{1}={2}\t", i, j, i * j);
                }
                //j每9次换行一次
                Console.WriteLine();
            }
             
           //下三角
            for (int i = 1; i < 10; i++)
            {
                for (int j = i; j <= 9; j++)
                {
                    Console.Write("{0}*{1}={2}  ", i, j, i * j);
                }
                Console.WriteLine();
            }
          //矩形乘法表
            //I 为乘法的第一个数
               for (int i = 1; i <= 9; i++)
            {
                //j为乘法的第二个数       
                for (int j = 1; j <= 9; j++)
                {
                    Console.Write("{0}*{1}={2}\t", i, j, i * j);
                }
                //j每9次换行一次
                Console.WriteLine();
            }

            Console.ReadKey();
        }
    }
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            int k = 0;
            Console.WriteLine("直角在左下角");
            for (int i = 1; i < 10; i++)   //直角在左下角
            {
                for (int j = 1; j <= i; j++)
                {
                    Console.Write("{0}*{1}={2}\t", j, i, i * j);
                }
                Console.WriteLine();
            }
            Console.WriteLine();//换行
            Console.WriteLine("直角在左上角");
            for (int i = 9; i > 0; i--)    //直角在右下角
            {
                for (int j = 1; j <= i; j++)
                {
                    Console.Write("{0}*{1}={2}\t", j, i, i * j);
                }
                Console.WriteLine();
            }
            Console.WriteLine();
            Console.WriteLine("直角在右上角");
            for (int i = 9; i > 0; i--)    //直角在右上角
            {
                for (int j = i; j > 0; j--)
                {
                    Console.Write("{0}={1}*{2}\t", i * j, i, j);
                }
                Console.WriteLine();
                for (k = 10 - i; k > 0; k--)
                {
                    Console.Write("\t");
                }
            }
            Console.WriteLine();
            Console.WriteLine("直角在右下角");
            for (int i = 1; i < 10; i++)    //直角在右下角
            {
                for (k = 9 - i; k > 0; k--)
                {
                    Console.Write("\t");
                }
                for (int j = i; j > 0; j--)
                {
                    Console.Write("{0}={1}*{2}\t", i * j, j, i);
                }
                Console.WriteLine();
            }
            Console.WriteLine();
              Console.ReadKey();
        }
    }
}

效果图