Main.cc: In function 'bool isPrime(int)':
Main.cc:16:13: error: 'sqrt' was not declared in this scope
   16 |    int tmp =sqrt(num);
      |             ^~~~
Main.cc: In function 'int main()':
Main.cc:33:13: warning: unused variable 'm' [-Wunused-variable]
   33 |         int m;
      |             ^