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switch problem

lyn18 (7)
this is part of the codes for my matrix problem.
when i run the codes, only Inverse matrix is working, but the button for Upper Triangular, and determinant are not working. i think it's because i make them in switch, and there is flag for each cases. but i don't know how to write the right codes to display the results based on the flags. 

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void CA5::OnInverse()
{
	flag=1;
	Compute();
}

void CA5::OnUpperTri()
{
	flag=2;
	Compute();
	
}

void CA5::OnDeterminant()
{
	flag=3;
	Compute();	
	
}


void CA5::Compute()
{
	GetInput();
	CString s;
	double B[N+1][N+1], X[N+1][N+1], g[N+1][N+1]; 
	double Sum,m,q,p,product;
	
	switch(flag)
	{
	case 1:
	{
		GetInput();
		CString s;
		
	//identity matrix 
		for (i=1; i<=N; i++)
			for (j=1; j<=N; j++)
			{
				if (i==j)
					B[i][j]=1;
				else
					B[i][j]=0;
			}

		// row operations
		for (k=1;k<=N-1;k++)
			for (i=k+1;i<=N;i++)
			{
				m=a[i][k]/a[k][k];
				for (j=1;j<=N;j++)
				{
					a[i][j] -= m*a[k][j];
					B[i][j] -= m*B[k][j];
				}
			}
		// backward substitutions
		for (i=N;i>=1;i--)
			for (j=1;j<=N;j++)
			{
				Sum=0;
				for (k=i+1;k<=N;k++)
					Sum += a[i][k]*X[k][j];
				X[i][j]=(B[i][j]-Sum)/a[i][i];
			}
	}

		break;

		
	case 2:
	{
		//uppertringular
		//row operations
		
		for (k=1; k<=N-1; i++)
			for (i=k+1; i<=N; i++)
			{
				q=a[i][k]/a[k][k];
				for(j=1;j<=N;j++)
					g[i][j] -=q*a[k][j];
			}
	}
		
		break;

		
	case 3:
	{
		//determinant
		//row operations
		
		for (k=1; k<=N-1; k++)
			for (i=k+1; i<=N; i++)
			{
				p=a[i][k]/a[k][k];
				for (j=1; j<=2; j++)
					a[i][j]-=p*a[k][j];
			}
		product=1;
		for (i=1; i<=N; i++)
			product *=a[i][i];

	}
		break;
	
	}
//displayresult for all 3 cases
	// case 1
	
	for (i=1;i<=N;i++)
	{
		for (j=1;j<=N;j++)
		{
			s.Format(L"%lf",X[i][j]);
			sa1[i][j].SetWindowText(s);
		}
	}

	// case 2
	
	for (i=1;i<=N;i++)
	{
		for (j=1;j<=N;j++)
		{
			s.Format(L"%lf",g[i][j]);
			sa2[i][j].SetWindowText(s);	
		}
	}
	
//case 3
	s.Format(L"%lf",product); sa3.SetWindowText(s);

}
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