foo.cc: In function 'int f(int)':
foo.cc:4:6: warning: unused variable 'x' [-Wunused-variable]
  int x;
      ^
foo.cc: In function 'int main()':
foo.cc:19:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
  ~~~~~^~~~~~~~~

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