Count letters in a file VB.Net Exercise - Visual Basic Programming Course

Imports System
Imports System.IO
Namespace ConsoleApplication1
    Class CountLetters
        Private Shared Sub Main()
            Dim debug As Boolean = True
            Console.Write("Name of file: ")
            Dim nameFile As String = Console.ReadLine()
            Console.Write("Letter for count: ")
            Dim letter As String = Console.ReadLine()
            Dim myfile As StreamReader
            myfile = File.OpenText(nameFile)
            Dim line As String
            Dim countLetter As Integer = 0

            Do
                line = myfile.ReadLine()

                If line IsNot Nothing Then

                    For i As Integer = 0 To line.Length - 1
                        If line.Substring(i, 1) = letter Then countLetter += 1
                    Next
                End If
            Loop While line IsNot Nothing

            myfile.Close()
            Console.WriteLine("Amount of letter: {0}", countLetter)
            If debug Then Console.ReadLine()
        End Sub
    End Class
End Namespace