foo.cc:8:5: error: ISO C++ forbids declaration of 'yh' with no type [-fpermissive]
    8 |  yh()
      |     ^
foo.cc:13:5: error: expected class-name before '(' token
   13 |  ~yh(){}
      |     ^
foo.cc: In member function 'int RPN::yh()':
foo.cc:12:2: warning: no return statement in function returning non-void [-Wreturn-type]
   12 |  }
      |  ^
foo.cc: In function 'int main()':
foo.cc:83:2: error: 'yh' was not declared in this scope
   83 |  yh r;
      |  ^~
foo.cc:84:8: error: 'r' was not declared in this scope
   84 |  cout<<r.Val(data)<<endl;
      |        ^

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