[C++] Lỗi toán tử nhân 2 ma trận

[rabbit]

Mình viết chương trình sử dụng các toán tử +,-,*,/ 2 ma trận. Lỗi xảy ra ở toán tử nhân 2 ma trận, khi nhân 2 ma trận từ cấp 3 trở lên là bị lỗi. Còn cấp 1, 2 vẫn bình thường. Các bạn xem giúp.

class MT
{
	int m, n;
	int **a;
public:
	MT()	{ m=0; n=0; a=NULL;}	// hàm tạo mặc định
	MT( int m1, int n1, int x=0);	// hàm tạo có tham số
	MT( const MT &);				// hàm tạo chép
	const MT & operator = (const MT &);		// toán tử gán
	friend MT operator + ( MT &, MT &);
	friend MT operator * ( MT &, MT &);
	friend int operator == (MT &, MT &);
	friend istream & operator >> ( istream &, MT &);
	friend ostream & operator << ( ostream &, MT &);
	void xoabonho();
	~MT();
};

MT::MT( int m1, int n1, int x)
{
	m= m1; n= n1;
	a= new int *[m];
	for( int i=0; i< m; i++)
		a[i]= new int [n];	
	for( int i=0; i<m; i++)
		for( int j=0; j< n; j++)
			a[i][j]=x;
}

MT::MT( const MT &A)
{
	m= A.m; n= A.n;
	a= new int *[m];
	if( a==NULL)
		cout<<"\nKhong du bo nho.";
	for( int i=0; i< m; i++)
		a[i]= new int [n];
	for ( int i=0; i< m; i++)
		for( int j=0; j< n; j++)
			a[i][j]= A.a[i][j];
}

void MT::xoabonho()
{
	if(a)
	{
		for( int i=0; i< m; i++)
			delete []a[i];
		delete []a;
	}
}

MT::~MT()
{
	xoabonho();
}
const MT & MT::operator = ( const MT &B)
{
	if( m != B.m || n != B.n)
	{
		xoabonho();
		m= B.m; n=B.n;
		a= new int *[m];
		if( a==NULL) 
			cout<<"\nKhong du bo nho.";
		for( int i=0; i< m; i++)
			a[i]= new int [n];
	}
	for( int i=0; i< m; i++)
		for( int j=0; j< n; j++)
			a[i][j]= B.a[i][j];
	return B;
}

MT operator + ( MT &B1, MT &B2)
{
	if( B1.m != B2.m || B1.n != B2.n)
	{
		cout<<"\nKhong cong duoc.";
		//exit(1);
	}
	MT A( B1.m, B1.n, 0);
	A.a = new int *[B1.m];
	for( int i=0; i< A.m; i++)
		A.a[i]= new int [B1.n];
	for( int i=0; i< A.m; i++)
		for( int j=0; j< A.n; j++)
			A.a[i][j]= B1.a[i][j] + B2.a[i][j];
	return A;
}

MT operator * ( MT &B1, MT &B2)
{
	if( B1.n != B2.m) 
	{
		cout<<"\nKhong nhan duoc.";
		//exit(1);
	}
	MT A( B1.m, B2.n, 0);
	A.a= new int *[B1.m];
	for( int i=0; i< A.m; i++)
		A.a[i]= new int [B2.n];
	for( int i=0; i< A.m; i++)
		for( int j=0; j< A.n; j++)
		{
			A.a[i][j] = 0;
			for( int k=0; k< A.n; k++)
				A.a[i][j] += B1.a[i][k] * B2.a[k][j];
		}
		return A;
}

int operator == ( MT &B1, MT &B2)
{
	int OK=1;
	if( B1.m != B2.m || B1.n != B2.n)
	{
		OK=0;
	}
	else
	{
		for( int i=0; i< B1.m; i++)
		{
			for( int j=0; j< B1.n; j++)
				if( B1.a[i][j] != B2.a[i][j])
					OK=0;
		}
	}
	return OK;
}

istream & operator >> ( istream & nhap, MT &A)
{
	do { cout<<"\nSo hang: ";  cin>> A.m;}
	while( A.m < 1 || A.m > 10);
	do { cout<<"So cot: ";  cin>> A.n;}
	while( A.n < 1 || A.n > 10);
	A.a= new int *[A.m];
	for( int i=0; i< A.m; i++)
		A.a[i]= new int [A.n];
	for( int i=0; i< A.m; i++)
		for( int j=0; j< A.n; j++)
		{
			cout<<"Nhap phan tu a["<<i<<"]["<<j<<"] : ";
			cin>>A.a[i][j];
		}
	return nhap;
}

ostream & operator << ( ostream & xuat, MT &A)
{
	for( int i=0; i< A.m; i++)
	{
		for( int j=0; j< A.n; j++)
			cout<<" "<<setw(4)<<A.a[i][j];
			cout<<"\n";
	}
	return xuat;
}

void menu()
{
	cout<<"\t\t MENU";
	cout<<"\n\t1. Nhap, xuat ma tran";
	cout<<"\n\t2. Cong 2 ma tran";
	cout<<"\n\t3. So sanh 2 ma tran";
	cout<<"\n\t4. Nhan 2 ma tran";
	cout<<"\n\t5. Gan ma tran";
	cout<<"\n\t0. Thoat";
}

void main()
{
	int chon;
	MT A,B,C;
	while(1)
	{
		do
		{
			menu();
			cout<<"\nChon chuc nang: ";
			cin>>chon;
		}
		while( chon < 0 || chon > 5);
		switch(chon)
		{
		case 1:
			{
				cout<<"\nNhap ma tran:";
				cin>>A;
				cout<<"\nXuat ma tran:\n";
				cout<<A;
				break;
			}
		case 2:
			{
				cout<<"\nNhap ma tran thu 2:";
				cin>>B;
				cout<<"Ma tran tong: \n";
				cout<<A+B;
				break;
			}
		case 3:
			{
				cout<<"\nSo sanh 2 ma tran: ";
				if( A==B) cout<<"2 ma tran bang nhau.\n";
				else cout<<"2 ma tran ko bang nhau.\n";
				break;
			}
		case 4:
			{
				cout<<"\nNhap ma tran thu 2:";
				cin>>B;
				cout<<"\nNhan 2 ma tran. Ma tran tich la: \n";
				cout<<A*B;
				break;
			}
		case 5:
			{
				cout<<"\nGan ma tran A cho C. Ma tran C:\n";
				C=A;
				cout<<C;
				break;
			}
		default: { exit(1); break;}
		}
		getch();
	}
}