VB.Net/Language Basics/Integer Parser

Validate an Integer

Imports System
Public Class MainClass
    
    Shared Sub Main(ByVal args As String())
        Dim num_items As Integer
        If Not IsValidInteger(num_items, "00", 1, 100) Then Exit Sub
        
    End Sub

    Shared     Private Function IsValidInteger(ByRef result As Integer, _
    ByVal txt As String, ByVal field_name As String, _
    Optional ByVal min_value As Integer = Integer.MinValue, _
    Optional ByVal max_value As Integer = Integer.MaxValue) As Boolean
        " Check for blank entry.
        If txt.Length < 1 Then
            Console.WriteLine("Please enter " & field_name & ".")
            Return False
        End If
        " See if it"s numeric.
        If Not IsNumeric(txt) Then
            Console.WriteLine(field_name & " must be a number.")
            Return False
        End If
        " Assign the value.
        Try
            result = Integer.Parse(txt)
        Catch ex As Exception
            Console.WriteLine("Error in " & field_name & "." & _
            vbCrLf & ex.Message)
            Return False
        End Try
        " Check that the value is between min_value and max_value.
        If result < min_value Or result > max_value Then
            Console.WriteLine(field_name & " must be between " & _
            min_value.ToString & " and " & max_value.ToString & ".")
            Return False
        End If
        " The value is okay.
        Return True
    End Function

End Class