矩阵运算C ++运算符重载程序错误

Class:

#include <string>
using namespace std;

class Matrix{
public:
float **grid;
Matrix(int r, int c);
friend istream& operator >>(istream& cin, Matrix & m );
void setMatrix();
void printMatrix();
friend ostream& operator <<(ostream& cout, Matrix & m);
private:
int row;
int column;

};

istream& operator >>(istream& cin, Matrix & m );
ostream& operator <<(ostream& cout, Matrix & m);
#include <string>
using namespace std;