foo.c:2:5: warning: conflicting types for built-in function 'nan'; expected 'double(const char *)' [-Wbuiltin-declaration-mismatch]
    2 | int nan(int ei)
      |     ^~~
foo.c:2:1: note: 'nan' is declared in header '<math.h>'
    1 | #include <stdio.h>
  +++ |+#include <math.h>
    2 | int nan(int ei)
foo.c: In function 'nan':
foo.c:4:8: warning: variable 'fan' set but not used [-Wunused-but-set-variable]
    4 |  int j,fan;
      |        ^~~
foo.c: In function 'main':
foo.c:28:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   28 |  scanf("%d",&n);
      |  ^~~~~~~~~~~~~~

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