C++编程出现点问题 求解答！！

有两个矩阵a和b，均为2行3列，编译程序，求两个矩阵之和。重载插入运算符“<<”和提取运算符“>>”,使之能用于该矩阵的输入输出。重载运算符“+”，使之能用于矩阵相加，如c=a+b。   我变得程序下   求和的结果有错！！！


#include<iostream>
using namespace std;
class JU{
public:
    JU()
    {a[0][0]=0;
     b[0][0]=0;
     c[0][0]=0;
    }
   
    int a_set()
    {int i,j;
     for( i=0;i<2;i++)
     {cout<<"a数组输入第"<<i+1<<"行："<<endl;
       for(j=0;j<3;j++)
       {cin>>a[i][j];}
     }
     return 0;
    }
    int b_set()
    {int i,j;
     for( i=0;i<2;i++)
     {cout<<"b数组输入第"<<i+1<<"行："<<endl;
       for(j=0;j<3;j++)
       {cin>>b[i][j];}
     }
     return 0;
    }
    friend JU operator+(JU &a1,JU &b1);
    friend ostream &operator<<(ostream &out,JU &obj);
    friend istream &operator>>(istream &in,JU &obj);
private:
    int a[2][3];
    int b[2][3];
    int c[2][3];
};
ostream &operator<<(ostream &out,JU &obj)
{out<<obj.a_set();
 return out;
}
istream &operator>>(istream &in,JU &obj)
{    return in;}
 JU operator+(JU &a1,JU &b1)
 {JU temp;
  int i,j;
  for(i=0;i<2;i++)
      for(j=0;j<3;j++)
      {temp.c[i][j]=a1.a[i][j]+b1.b[i][j];
        cout<<temp.c[i][j]<<" ";
      }
  return temp;
 }
void main()
{JU ob_a,ob_b,sum;
cout<<ob_a<<endl;
cout<<ob_b<<endl;
sum=ob_a+ob_b;
}