有两个矩阵A和B，均为3行4列，求两个矩阵之和。重载运算符+和-，实现两个矩阵想加和想减

#define maxh 100
#include <iostream>
using namespace std;

class Matrix { public:
int r, c;
int s[maxh][maxh];
Matrix operator + ( const Matrix &b );
Matrix operator - ( const Matrix &b );
};

Matrix Matrix :: operator + ( const Matrix &b )
{
Matrix res; res.r = r, res.c = c;
for ( int i = 0; i < r; i ++ )
for ( int j = 0; j < c; j ++ )
res.s[i][j] = s[i][j] + b.s[i][j];
return res;
}

Matrix Matrix :: operator - ( const Matrix &b )
{
Matrix res; res.r = r, res.c = c;
for ( int i = 0; i < r; i ++ )
for ( int j = 0; j < c; j ++ )
res.s[i][j] = s[i][j] - b.s[i][j];
return res;
}

Matrix a, b, c;

int main ( )
{
a.r = 4; b.r = 4;
a.c = 3; b.c = 3;
for ( int i = 0; i < a.r; i ++ )
for ( int