c++ 为什么输出的是垃圾值？

#include<iostream.h> #include<math.h> class student{ friend class teacher; private:int id,clas; int math,physics; public: student(int id,int clas,int math,int physics) { id=id; clas=clas; math=math; physics=physics; } }; class teacher{ public : int sum1; teacher(student &a,student &b){ if(a.clas==1){ sum1+=a.math; } if(b.clas==1){ sum1+=b.math; } cout<<sum1<<endl; } }; voi

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