open a window according to the type chosen in mainwindow

[d_stranz]

I think anda_skoa means something like this:

// pseudocode
void MainWindow::on_pushButton_3_clicked()
{
    switch ( userType )
    {
        case User:
             showUserWindow();
             break;
 
        case Doctor:
             showDoctorWindow();
             break;
 
        case Administrator:
             showAdminWindow();
             break;
 
        default:
             // error - no such user type
             break;
    }
}

// pseudocode
void MainWindow::on_pushButton_3_clicked()
{
    switch ( userType )
    {
        case User:
             showUserWindow();
             break;

        case Doctor:
             showDoctorWindow();
             break;

        case Administrator:
             showAdminWindow();
             break;

        default:
             // error - no such user type
             break;
    }
}

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Obviously, your code will store the "userType" based on the previous button the user clicked.

By the way, "pushButton_3" is a pretty bad name for a variable. A year from now, when you have to fix something in this code, will you remember which GUI button is the one named "pushButton_3" in the code? You'd probably have a much easier job if it were named "connectButton" or "joinButton" instead.