foo.cc: In function 'int main()':
foo.cc:6:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&k);
  ~~~~~^~~~~~~~~
foo.cc:11:5: warning: 'sn' may be used uninitialized in this function [-Wmaybe-uninitialized]
   sn+=1/i;
   ~~^~~~~