foo.cc: In function 'void cx()':
foo.cc:60:6: error: '_v' was not declared in this scope
   60 |  if (_v[n]==false){
      |      ^~
foo.cc:55:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   55 |  scanf("%lld",&n);
      |  ~~~~~^~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:79:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   79 |  scanf("%lld",&T);
      |  ~~~~~^~~~~~~~~~~

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