foo.cc: In function 'void tarjan(int)':
foo.cc:17:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<ver[x].size(); i++) {
               ~^~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:41:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a);
   ~~~~~^~~~~~~~~
foo.cc:45:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%d",&a);
    ~~~~~^~~~~~~~~

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