foo.cc: In function 'int main()':
foo.cc:16:5: warning: unused variable 'n' [-Wunused-variable]
   16 | int n;
      |     ^
foo.cc:19:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   19 | scanf("%d",&arr[i].id);
      | ~~~~~^~~~~~~~~~~~~~~~~

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