foo.cc:14:12: warning: multi-character character constant [-Wmultichar]
      cout<<'YES'<<endl;
            ^~~~~
foo.cc:15:17: warning: multi-character character constant [-Wmultichar]
      else cout<<'NO'<<endl;
                 ^~~~
foo.cc: In function 'int main()':
foo.cc:7:21: error: 'x' was not declared in this scope
    int a,b,c;  cin>>x;
                     ^

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