foo.c: In function 'main':
foo.c:29:6: error: 'i' undeclared (first use in this function)
   29 |  for(i=1;i<=n;i++)
      |      ^
foo.c:29:6: note: each undeclared identifier is reported only once for each function it appears in
foo.c:31:7: error: 'j' undeclared (first use in this function)
   31 |   for(j=1;j<=n;j++)
      |       ^
foo.c:58:8: error: 'side_lenth' undeclared (first use in this function)
   58 |     if(side_lenth*side==sum)
      |        ^~~~~~~~~~
foo.c:70:23: warning: format '%d' expects argument of type 'int', but argument 2 has type 'int *' [-Wformat=]
   70 |  printf("边长为：%d",&side);
      |                      ~^  ~~~~~
      |                       |  |
      |                       |  int *
      |                       int
      |                      %ls

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