3.b.ファイルから読み込んだ文字列を逆順に出力できません。

やりたいことは以下のとおりです。ファイル data01.in から読み込んだ文字列を逆順に data03.out に書き出すようにしたいです。
data01.inとdata03.outの中身を確認したら両方とも同じでした。どうすればできるようになりますか？

Source
1#include <stdio.h>
2    #include <stdlib.h>
3
4
5    #define MAX 1000
6
7    int main ()
8    {
9      char in_filename [] = "data01.in";
10
11      char out_filename [] = "data03.out"
12;
13      FILE * fpin, * fpout;
14
15      char buf [MAX];
16      int c;
17      int n;
18      int i;
19
20      / * Open the input file. * /
21      if ((fpin = fopen (in_filename, "r")) == NULL)
22      {
23        printf ("Failed to open:% s \ n", in_filename);
24        exit (1);
25      }
26
27      / * Open the output file. * /
28      if ((fpout = fopen (out_filename, "w")) == NULL)
29      {
30        printf ("Failed to open:% s \ n", out_filename);
31        fclose (fpin);
32        exit (2);
33      }
34
35
36      / * Read data up to the maximum number of buffers * /
37      for (n = 0; n <MAX; ++ n)
38      {
39        if ((c = fgetc (fpin)) == EOF)
40          break;
41
42        buf [n] = (char) c; / * Don't forget to cast to char. * /
43      }
44
45      / * If EOF is not reached even after the maximum number of buffers is reached, an error is processed as buffer overflow.
46      * /
47      if (n == MAX)
48      {
49        printf ("Buffer overflow! \ N");
50        exit (3);
51      }
52
53      / * Output the contents of the buffer. * /
54      for (i = 0; i <n; ++ i)
55      {
56        fputc (buf [i], fpout);
57      }
58
59      / * Don't forget to close each opened I / O file. * /
60      fclose (fpout);
61      fclose (fpin);
62
63      return 0;
64    }