diff --git a/functions.c b/functions.c
index 94ceab9..f5d564f 100644
--- a/functions.c
+++ b/functions.c
@@ -89,8 +89,8 @@ void player_act(char arr[3][3])  //
         scanf("%d,%d", &x, &y);
         if(arr[--x][--y] == ' ')
         {
-                arr[x][y] = 'O';
-                break;
+            arr[x][y] = 'O';
+            break;
         }
         else
         {
@@ -99,7 +99,7 @@ void player_act(char arr[3][3])  //
         }
     }
 }
-void computer_act(char arr[3][3])  //电脑行动
+void computer_act_easy(char arr[3][3])  //电脑行动
 {
     srand((unsigned)time(NULL));//用系统时间初始化随机数种子
     while (1)//无限循环直到遇到break退出
@@ -113,3 +113,54 @@ void computer_act(char arr[3][3])  //
         }
     }
 }
+void mode()
+{
+    printf("****************************\n");
+    printf("**       1. 简单模式      **\n");
+    printf("**       2. 困难模式      **\n");
+    printf("****************************\n");
+}
+
+void computer_act_hard(char arr[3][3])
+{
+    int value[3][3];
+    int i, j, m, count_X, count_O, count_;
+    for(i = 0; i < 3; i++)
+    {
+        for(j = 0; j < 3; j++)
+        {
+            if(arr[i][j] == ' ')
+            {
+                if(i - j == 1 || j - i == 1) //不在对角线上的点
+                {
+                    for(m = 0; m < 3; m++)
+                        arr[i][m] == 'O' ? count_O++ : arr[i][m] == 'X' ? count_X++ : count_++;
+                    if(count_X == 2) value[i][j] = 6;
+                    else if(count_O == 2) value[i][j] = 5;
+                    else if(count_X == 1 && count_ == 1) value[i][j] = 4;
+                    else if(count_O == 1 && count_ == 1) value[i][j] = 3;
+                    else if(count_ == 2) value[i][j] = 2;
+                    else value[i][j] = 1;
+                    count_O = count_X = count_ = 0;
+                    for(m = 0; m < 3; m++)
+                        arr[m][j] == 'O' ? count_O++ : arr[m][j] == 'X' ? count_X++ : count_++;
+                    if(count_X == 2) value[i][j] = 6;
+                    else if(count_O == 2) value[i][j] = 5;
+                    else if(count_X == 1 && count_ == 1) value[i][j] = 4;
+                    else if(count_O == 1 && count_ == 1) value[i][j] = 3;
+                    else if(count_ == 2) value[i][j] = 2;
+                    else value[i][j] = 1;
+                    count_O = count_X = count_ = 0;
+                }
+                /*else if()
+                {
+
+
+                }*/
+            }
+            else
+                value[i][j] = 0;
+
+        }
+    }
+}
diff --git a/main.c b/main.c
index a8a7a94..be1aee3 100644
--- a/main.c
+++ b/main.c
@@ -2,55 +2,79 @@
 #include <time.h>
 #include <stdlib.h>
 #include "sanziqi.h"
-#define computer_first 1
-#define player_first 0
 int main()   //主函数
 {
-    char arr[3][3];
+    char arr[3][3], ch;
     while(1)
     {
         menu();
-        int i=0;
-        scanf("%d",&i);
-        if(i)
+        int i = 0;
+        scanf("%d", &i);
+        if(i == start_game)
         {
+            int choice = 0;
+            mode();
             init_board(arr);
-            print_board(arr);
-            if(whom_act()==computer_first)
+            if(scanf("%d", &choice) == 1)
             {
-                while(i++<9)
+                switch(choice)
                 {
-                    computer_act(arr);
+                case 1:
                     print_board(arr);
-                    if(judge(arr)=='X') break;
-                    player_act(arr);
-                    print_board(arr);
-                    if(judge(arr)=='O') break;
+                    if(whom_act() == computer_first)
+                    {
+                        while(i++ < 9)
+                        {
+                            computer_act_easy(arr);
+                            print_board(arr);
+                            if(judge(arr) == 'X') break;
+                            player_act(arr);
+                            print_board(arr);
+                            if(judge(arr) == 'O') break;
+                        }
+                        if(judge(arr) == 'O')
+                            printf("你赢了。\n");
+                        else if(judge(arr)=='X')
+                            printf("你输了。\n");
+                        else
+                            printf("平局");
+                    }
+                    else
+                    {
+                        while(i++ < 9)
+                        {
+                            player_act(arr);
+                            print_board(arr);
+                            if(judge(arr) == 'O') break;
+                            computer_act_easy(arr);
+                            print_board(arr);
+                            if(judge(arr) == 'X') break;
+                        }
+                        if(judge(arr) == 'O')
+                            printf("你赢了。\n");
+                        else if(judge(arr)=='X')
+                            printf("你输了。\n");
+                        else
+                            printf("平局\n");
+                    }
+                    break;
+                case 2:
+                    computer_act_hard(arr);
+                    break;
+                default:
+                    printf("wrong input！请重新输入\n");
                 }
-                if(judge(arr)=='O')
-                    printf("你赢了。\n");
-                else
-                    printf("你输了。\n");
             }
             else
             {
-                while(i++<9)
-                {
-                    player_act(arr);
-                    print_board(arr);
-                    if(judge(arr)=='O') break;
-                    computer_act(arr);
-                    print_board(arr);
-                    if(judge(arr)=='X') break;
-                }
-                if(judge(arr)=='O')
-                    printf("你赢了。\n");
-                else
-                    printf("你输了。\n");
+                while ((ch = getchar()) != EOF && ch != '\n');//清空缓存区，防止scanf接收上次的非法输入从而死循环
+                printf("wrong input！请重新输入\n");
             }
         }
-        else
+        else if(i == end_game)
             break;
+        else
+            printf("wrong input！请重新输入\n");
     }
     return 0;
 }
diff --git a/sanziqi.h b/sanziqi.h
index 339ea22..4b26e80 100644
--- a/sanziqi.h
+++ b/sanziqi.h
@@ -3,6 +3,11 @@
 #include <time.h>
 #include <stdio.h>
 #include <stdlib.h>
+#define computer_first 1
+#define player_first 0
+#define start_game 1
+#define end_game 0
+void mode();
 
 void init_board(char arr[3][3]);  //初始化棋盘
 
@@ -18,8 +23,9 @@ char judge(char arr[3][3]);  //
 
 void player_act(char arr[3][3]);  //玩家行动
 
-void computer_act(char arr[3][3]);  //电脑行动
+void computer_act_easy(char arr[3][3]);  //电脑行动
 
+void computer_act_hard(char arr[3][3]);
 
 
 #endif // SANZIQI_H_INCLUDED