c++问题，为什么发生错误

Question

#include<iostream>using namespace std;class Vector{ float v[4]; float sum; friend class vectorContainer;public: Vector(float ve[]){  sum=0;  for(int i=0;i<4;i++)  {   v[i]=ve[i];   sum=sum+v[i];  }  }Vector(){ for(int i=0;i<4;i++)         v[i]=0; } ~Vector(){} void output(); Vector& operator=(Vector &a);};void Vector::output(){ for(int i=0;i<4;i++) {  cout << v[i] << " " ;  } cout << sum << endl ;}Vector& Vector::operator=(Vector &a){      for(int i=0;i<4;i++)   {         v[i]=a.v[i];   }   sum=a.sum;      return *this;}class vectorContainer{ Vector* _v; int _size;public: vectorContainer(Vector *ve,int size){  _v=new Vector[size];  _size=size;  for(int i=0;i<size;i++)   _v[i]=ve[i];} vectorContainer(){} ~vectorContainer(){}Vector& operator[](int idx); Vector* operator->(); void operator()(); Vector& operator()(int i); float& operator()(int i,int j);};Vector& vectorContainer::operator[](int idx){ _v=_v+idx; for(int j=0;j<4;j++)  cout << _v->v[j] << " " ; cout << endl; _v=_v-idx; return *_v;}Vector* vectorContainer::operator->(){ Vector *big; big=_v[0]; for(int i=1;i<_size;i++) {  if(big.sum<_v[i].sum)        big=_v[i]; }    return big;}int main(){Vector a0[4]; float k1[]={1,2,3,4}; float k2[]={2,3,4,5}; float k3[]={3,4,5,6}; float k4[]={4,5,6,7};Vector a1(k1); Vector a2(k2); Vector a3(k3); Vector a4(k4);a0[0]=a1; a0[1]=a2; a0[2]=a3; a0[3]=a4; vectorContainer c(a0,4); c[0]; c[1]; c[2]; c[3];c->output();}在重载—>的时候发生了不知道什么错误，麻烦帮帮我改1下，请详细解释，我已经重载了=号，并且在重载【】时验证了是正确的