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Thread: Problem with conditional statements

  1. #1

    Thread Starter
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    Join Date
    Mar 2012
    Posts
    4

    Problem with conditional statements

    Code:
    Imports System.IO
    Public Class Form1
        Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLogin.Click
            Dim alltext() As String = System.IO.File.ReadAllLines("C:\Users\Parent\Documents\Visual Studio 2008\Projects\Members.txt")
            Dim lookfor As String = txtLogin.Text & ","
    
            If txtLogin.Text = "Admin" And txtPassword.Text = "DWADMIN" Then
                MsgBox("You are now successfuly logged in")
                Form2.Show()
                Me.Hide()
                'generic admin login for all staff
            End If
    
            For Each line As String In Filter(alltext, lookfor)
                If line.StartsWith(txtLogin.Text) Then
                    MsgBox("You are now successfully logged in")
                    Form3.Show()
                    Me.Hide()
                End If
            Next      
    
            If txtLogin.Text = "" Or txtPassword.Text = "" Then
                MsgBox("Please enter Username/Password")
            End If
    Right basically I'm having trouble using if and elseif statements. I cant use these three small pieces of code because I constantly get 'Else must be preceded by an If or ElseIf' but there is nowhere for me to put these without these erroring?

  2. #2
    Super Moderator Shaggy Hiker's Avatar
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    Idaho
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    Re: Problem with conditional statements

    I'm not fully clear on what you are trying to do, but something like this seems more likely:

    Code:
    If txtLogin.Text = "" OrElse txtPassword.Text = "" Then
                MsgBox("Please enter Username/Password")
    ElseIf txtLogin.Text = "Admin" AndAlso txtPassword.Text = "DWADMIN" Then
                MsgBox("You are now successfuly logged in")
                Form2.Show()
                Me.Hide()
                'generic admin login for all staff
    Else
     For Each line As String In Filter(alltext, lookfor)
                If line.StartsWith(txtLogin.Text) Then
                    MsgBox("You are now successfully logged in")
                    Form3.Show()
                    Me.Hide()
                End If
            Next      
    End If
    I'm taking a big guess with where that For Loop went. I figured that you wanted to require something in both textboxes, and if either was empty, scold the user. That's the If part. Next, if there were specific things in the textboxes, check to see whether they are the Admin credentials. That's the ElseIf part. Finally, if there was something in the textbox, and it wasn't the admin credentials, use the For loop to check the file. That's the Else part.
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  3. #3
    Addicted Member EilaDoll's Avatar
    Join Date
    Dec 2011
    Posts
    147

    Re: Problem with conditional statements

    Please show the code with the "elseif" statements that is causing the error, we can't help if we can't see the broken part.

  4. #4
    .NUT jmcilhinney's Avatar
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    Sydney, Australia
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    96,580

    Re: Problem with conditional statements

    So many people seem to either forget or ignore that programming doesn't exist in a vacuum. Code is an implementation of a solution to a real-world problem. It is AN IMPLEMENTATION OF A SOLUTION, it is NOT the solution itself. Looking at Shaggy's code from post #2, that can easily be described in simple English:
    If the login and password text boxes are empty then notify the user of the error, otherwise if the login and password text boxes contain "Admin" and "DWADMIN" respectively then notify the user that they're logged in and proceed, otherwise loop through a list of user names and if the line starts with the contents of the contents of the login text box then notify the user that they're logged in and proceed.
    That is the solution. The reason that you and so many other people have problems is because you're trying to implement the solution without a clear understanding of what the solution is that you're trying to implement. There's very little chance of the code you write doing what you want it to do if you don't know what it is that you want it to do.

    You should be doing things the other way around. You should be picking up a pen and paper (remember those?) and writing out the solution, something like what I provided above. From that, you can then write pseudo-code that implements that solution. I'm assuming that beginner courses still teach pseudo-code and everyone still ignores it. Once you have the pseudo-code you can actually run through it manually with some inputs and outputs to make sure that it works in all situations. Only then should you approach the keyboard and start to write actual VB code. At that point you will have a very clear understanding of what the code has to do so, while there may still be issues, you won;t have large chunks of code in completely the wrong order.
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