Visual Studio 2019 MFC C++ Make button open another dialog box?

Question

I have a Dialog-based MFC app, and it has two Dialog Boxes:

1. IDD_FITNESSAPP_LOGIN_DLG
2. IDD_FITNESSAPP_MAIN_DLG

On IDD_FITNESSAPP_LOGIN_DLG , I have a button, btnLogin , that runs through some credentials (working so far, and reports failures too).

How do I make it so that when I click btnLogin on IDD_FITNESSAPP_LOGIN_DLG , it leads to IDD_FITNESSAPP_MAIN_DLG ?

I read a little on Dlg.DoModal() but I don't understand that if its needed.

Here's the code for the "on button clicked btnLogin ":

void CFitnessAppMFC2Dlg::OnBnClickedbtnlogin()
{
    // TODO: Add your control notification handler code here
    UpdateData();

    char UsernameFromFile[20], PasswordFromFile[20];
    FILE* fleCredentials;
    bool ValidLogin = false;

    if (m_Username == "")
    {
        AfxMessageBox(_T("You must provide a username and a password or click Cancel"));
        return;
    }
    if (m_Password == "")
    {
        AfxMessageBox(_T("Invalid Login"));
        return;
    }

    try {
        // Open the file for reading
        fleCredentials = fopen("credentials.txt", "r");

        // Scan the file from beginning to end
        while (!feof(fleCredentials))
        {
            // Read a username
            fscanf(fleCredentials, "%s", UsernameFromFile);

            // Compare the typed username with the username from the file
            CT2A ascii(m_Username);
            if (strcmp(ascii, UsernameFromFile) == 0)
            {
                // With the current username, retrieve the corresponding password
                fscanf(fleCredentials, "%s", PasswordFromFile);

                // Compare the typed password with the one on file
                CT2A ascii2(m_Password);
                if (strcmp(ascii2, PasswordFromFile) == 0)
                {
                    ValidLogin = true;
                }
                else
                    ValidLogin = false;
            }
        }
        if (ValidLogin == true)
            OnOK();
        else
        {
            AfxMessageBox(_T("Invalid Credentials. Please try again"));
            this->m_EditUsername.SetFocus();
        }

        fclose(fleCredentials);
    }
    catch (...)
    {
        AfxMessageBox(_T("Could not validate the credentials"));
    }

    UpdateData(FALSE);
}

Answer 1

1. Resourse View-> Dialog->Right click->Add Resource->Dlg , Then add class for the new Dlg.

2.There are two types of Dlgs.

Modal Dialogue Box

When the user wants to operate on applications other than the dialog box, the dialog box must first be responded to.

 #include "CXXXDlg.h "

 void CXXXDlg::OnBnClickedOk() 
 {   
     CMyNewDlg  Dlg;   
     Dlg.DoModal(); 
 }

Modeless Dialogue Box

When the user opens a non-modal dialog box, other windows can still be operated.

#include "CXXXDlg.h"

void CXXXDlg::OnBnClickedOk()
{
    CMyNewDlg  *pDlg=new CMyNewDlg ;
    pDlg->Create(IDD_DIALOG2,this);
    pDlg->ShowWindow(SW_SHOW);
}