What wrong with my code "Filling up the text box depending to the value of a combo box"??

I have a combo box that have a value of "Internet, Games, print (short), print (long)"... All I want is if I choose Internet in the combo box the text box "t_amount" should populate as "20"

here's my code...

Private Sub C_job_SelectedIndexChanged(sender As Object, e As EventArgs) Handles C_job.SelectedIndexChanged
    If C_job.SelectedIndex = "Internet" Then
        t_amount.Text = "20"
    ElseIf C_job.SelectedIndex = "Games" Then
        t_amount.Text = "10"
    ElseIf C_job.SelectedIndex = "Print (short)" Then
        t_amount.Text = "1"
    ElseIf C_job.SelectedIndex = "Print (long)" Then
        t_amount.Text = "2"
    End If
End Sub

You already have an answer, but I think the code can be improved upon a little. As a rule of thumb, if I'm going to be doing a check against a single variable for more than a couple items in a list, I use Select Case rather than an ongoing list of ElseIf statements. The number one reason being that if you change something on the first one, you'll have to remember to change it on all the others. CodeGray has solved some of this issue by declaring the value as a local variable, but the readability still stands to gain, so try this instead:

Select Case C_job.SelectedItem.ToString
	Case "Internet"
		t_amount.Text = "20"
	Case "Games"
		t_amount.Text = "10"
	Case "Print (short)"
		t_amount.Text = "1"
	Case "Print (long)"
		t_amount.Text = "2"
End Select

Also, i just wanted to check that you were using the Display Member and the Value Member of the ComboBox correctly. You can expose two properties with native support in combo boxes, one a value to display to the user, and a second a backing property. When you're executing code, you'll have access to both. The plus side is you can store this information in a more declarative way and then react accordingly.

When the ComboBox has a selection, that information is stored in the SelectedItem property which stores the original object used to populate that drop down item. If you've defined a DisplayMember and ValueMember for combo box items, then the SelectedText and SelectedValue will expose just those properties for the selected object.

Here's the Setup

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim dataSource As New DataTable

    With dataSource.Columns
        .Add("Display", GetType(String))
        .Add("Value", GetType(Integer))
    End With

    With dataSource.Rows
        .Add("Internet", 20)
        .Add("Games", 10)
        .Add("Print (short)", 1)
        .Add("Print (long)", 2)
    End With

    With C_job
        .DisplayMember = "Display"
        .ValueMember = "Value"
        .DataSource = dataSource
    End With
End Sub

The plus side, is now here's all the code you need to handle the event

Private Sub C_job_SelectedIndexChanged(sender As Object, e As EventArgs) Handles C_job.SelectedIndexChanged
    t_amount.Text = C_job.SelectedValue
End Sub

If you wanted to, this will also make binding this property very easy since you've coded all your logic upfront.