foo.cc: In function ‘bool isPrime(long long int)’:
foo.cc:15:25: error: ‘sqrt’ was not declared in this scope
   15 |         long long tmp = sqrt(num);
      |                         ^~~~
foo.cc: In function ‘int main()’:
foo.cc:32:26: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   32 |         for(int i = 0; i < v.size(); i++)
      |                        ~~^~~~~~~~~~