foo.cc: In function 'int main()':
foo.cc:14:20: error: 'x' was not declared in this scope
   14 |         if(isprime(x)) cout<<"Yes";
      |                    ^
foo.cc:12:15: warning: unused variable 'num' [-Wunused-variable]
   12 |         int n,num=0;
      |               ^~~

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