foo.cc: In function 'int is_prime(int)':
foo.cc:6:16: error: 'No' was not declared in this scope
         return No;
                ^~
foo.cc:8:16: error: 'Yes' was not declared in this scope
         return Yes;
                ^~~
foo.cc:12:20: error: 'No' was not declared in this scope
             return No;
                    ^~
foo.cc:14:12: error: 'Yes' was not declared in this scope
     return Yes;
            ^~~
foo.cc: In function 'int main()':
foo.cc:21:5: error: 'cin' was not declared in this scope
     cin>>x;
     ^~~
foo.cc:21:5: note: suggested alternative: 'main'
     cin>>x;
     ^~~
     main
foo.cc:24:25: error: 'Yes' was not declared in this scope
         if(is_prime(i)==Yes)
                         ^~~
foo.cc:27:5: error: 'cout' was not declared in this scope
     cout<<op<<endl;
     ^~~~
foo.cc:27:15: error: 'endl' was not declared in this scope
     cout<<op<<endl;
               ^~~~
foo.cc:27:15: note: suggested alternative: 'enum'
     cout<<op<<endl;
               ^~~~
               enum
foo.cc:29:5: error: 'system' was not declared in this scope
     system("pause");
     ^~~~~~