Const MAX_OCTET = 255
Const MIN_NETWORK = 1
Const MAX_NETWORK = 32
Const OCTET_BITS = 8

Type IPAddress
    octets(3) As Integer
End Type

Function isDigit(Byval ch As String) As Boolean
	Return (Asc(ch) >= Asc("0")) And (Asc(ch) <= Asc("9"))
End Function

Function ParseIPAddress(cidr As String, Byref networkWidth As Integer) As IPAddress
    Dim As IPAddress ip
    Dim As Integer slashPos = Instr(cidr, "/")
    Dim As String ipPart = Left(cidr, slashPos - 1)

    networkWidth = Val(Mid(cidr, slashPos + 1))

    Dim As Integer i, currentOctet = 0, octetValue = 0
    For i = 1 To Len(ipPart)
        If Mid(ipPart, i, 1) = "." Then
            ip.octets(currentOctet) = octetValue
            currentOctet += 1
            octetValue = 0
        Elseif IsDigit(Mid(ipPart, i, 1)) Then
            octetValue = octetValue * 10 + Val(Mid(ipPart, i, 1))
        End If
    Next
    ip.octets(currentOctet) = octetValue

    Return ip
End Function

Function ApplyNetworkMask(ip As IPAddress, networkWidth As Integer) As IPAddress
    Dim As IPAddress result = ip
    Dim As Integer completeOctets = networkWidth \ OCTET_BITS
    Dim As Integer remainingBits = networkWidth And 7

    ' Apply mask to partial octet
    If completeOctets < 4 Then
        result.octets(completeOctets) And= (MAX_OCTET - 2^(OCTET_BITS-remainingBits) + 1)
        ' Zero remaining octets
        For i As Integer = completeOctets + 1 To 3
            result.octets(i) = 0
        Next
    End If

    Return result
End Function

Function ValidateInput(ip As IPAddress, networkWidth As Integer, cidr As String) As Boolean
    If Instr(cidr, "/") = 0 Then
        Print "INVALID CIDR STRING: '"; cidr; "'"
        Return False
    End If

    If networkWidth < MIN_NETWORK Or networkWidth > MAX_NETWORK Then
        Print "INVALID NETWORK WIDTH:"; networkWidth
        Return False
    End If

    For i As Integer = 0 To 3
        If ip.octets(i) > MAX_OCTET Then
            Print "INVALID OCTET VALUE:"; ip.octets(i)
            Return False
        End If
    Next

    Return True
End Function

Sub ProcessCIDR(cidr As String)
    Dim As Integer networkWidth
    Dim As IPAddress ip = ParseIPAddress(cidr, networkWidth)

    If Not ValidateInput(ip, networkWidth, cidr) Then Exit Sub

    ip = ApplyNetworkMask(ip, networkWidth)

    Dim As String result = Str(ip.octets(0))
    For i As Integer = 1 To 3
        result &= "." & Str(ip.octets(i))
    Next
    Print result & "/" & networkWidth
End Sub

' Main program
Dim As String cidr(9) = { _
"87.70.141.1/22", "36.18.154.103/12", "62.62.197.11/29", _
"67.137.119.181/4", "161.214.74.21/24", "184.232.176.184/18", _
"127.0.0.1", "123.45.67.89/0", "98.76.54.32/100", "123.456.789.0/12" }

For i As Integer = 0 To 9
    ProcessCIDR(cidr(i))
Next

Sleep