Hide and unhide certain rows with certain value

I'm not so good with coding...

I need VBA macro for: a button that either hides or unhides rows when I click on it...
So, if rows are already hidden, then this button unhides them.
If those rows are not hidden, then it hides them.

The criteria what rows to hide/unhide is:
- Any rows that have the letter "r" within range ("C4:C350")

Please help!
Thanks!

Here try this

Private Sub cmdRow_Click()
Dim cell As Range

For Each cell In Range("C4:C350")
    If UCase(cell.Value) = "R" Then
        If Rows(cell.Row).Hidden Then
            Rows(cell.Row).Hidden = False
        Else
            Rows(cell.Row).Hidden = True
        End If
    End If
Next cell
End Sub

Thanks a lot JieJenn!!! it works, but

is there a way to make it go a little faster??? it seem like it's doing one row at a time...

I have a similar macro for another project, but the difference is it hides when the cell is "blank" (and it only hides, it doesn't unhide)... I notice that it has a "Union" function in it, I think this is the key to make it go faster... is there a way you can incorporate a similar function into the code you wrote?

 Dim RangeToHide As Range
 Dim rRowRange As Range

    Set rRowRange = Range("B4:B260")

    rRowRange.EntireRow.Hidden = False
    For Each rRow In rRowRange
        If Len(rRow.Value) = 0 Then
            If RangeToHide Is Nothing Then
                Set RangeToHide = rRow
            Else
                Set RangeToHide = Union(RangeToHide, rRow)
            End If
        End If
    Next rRow

    If Not RangeToHide Is Nothing Then
        RangeToHide.EntireRow.Hidden = True
    End If

Hum... the macro runs pretty fast on my PC. Anyway try the revision then.

Private Sub cmdRow_Click()
Dim cell As Range

For Each cell In Range("C4:C350").SpecialCells(xlCellTypeConstants)
    If UCase(cell.Value) = "R" Then
        If Rows(cell.Row).Hidden Then
            Rows(cell.Row).Hidden = False
        Else
            Rows(cell.Row).Hidden = True
        End If
    End If
Next cell
End Sub

I feel like I missing some really import information. Anyway, try again

Private Sub cmdRow_Click()
Dim cell As Range
With Application
.ScreenUpdating = False
For Each cell In Range("C4:C350").SpecialCells(xlCellTypeConstants, xlValue)
    If UCase(cell.Value) = "R" Then
        If Rows(cell.Row).Hidden Then
            Rows(cell.Row).Hidden = False
        Else
            Rows(cell.Row).Hidden = True
        End If
    End If
Next cell

.ScreenUpdating = True
End With
End Sub

Mine took about 0.5 seconds.

Here is a completed sample. THank you again!