Option Explicit On
Option Strict On

Public Class Form1

    Private Sub BT_CALCUL_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BT_CALCUL.Click
        LBL_COUT.Visible = False
        If Verification() Then
            LBL_COUT.Text = "Le cout du voyage sera de " & Calcul(TXT_CONSOMMATION.Text, TXT_NBKM.Text, Me.TXT_PRIXESS.Text) & " €"
            LBL_COUT.Visible = True
        End If
        LBL_ERR.Visible = Not LBL_COUT.Visible
    End Sub

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
        LBL_COUT.Visible = False
        LBL_ERR.Visible = False
    End Sub

    Function Verification() As Boolean
        If Not IsNumeric(Me.TXT_CONSOMMATION.Text) Then Return False
        If Not IsNumeric(Me.TXT_NBKM.Text) Then Return False
        If Not IsNumeric(Me.TXT_PRIXESS.Text) Then Return False
        Return True
    End Function

    Function Calcul(ByVal Consommation As String, ByVal NbKm As String, ByVal PrixEss As String) As Double
        Dim Cout As Double
        Cout = ((Val(NbKm) / 100) * Val(Consommation)) * Val(PrixEss)
        Return Cout
    End Function

    Private Function GetVal(ByVal Text As String) As Double
        Return Val(Text.Replace(",", "."))
    End Function

End Class