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