De l'aide en VB svp merci .(code)

Bonjour,
j'ai un probleme avec la parti multi des que je lance le programme quelq'un peut m'aidez ?
Module Module1

Sub Main()
Dim dev1 As String = 0
Dim dev2 As String = "Multi"
Dim dev3 As Integer = 0
Dim dev4 As Integer = 0
Dim dev5 As String = 0
Dim dev6 As Integer = 0
Dim dev7 As Integer = 0
Dim dev8 As Integer = 0
Console.Write("Welcome to Ultimate Calculator By Miodo")
Console.WriteLine("please choose a number to begin operation")
Console.WriteLine("tape -multi- for multiplicate a number and plusplus for addition")
dev1 = Console.ReadLine()
'premiere parti du programme addition
If dev1 = "plusplus" Then
Console.WriteLine("you choose " & dev1)
Console.WriteLine("write the first number please")
dev3 = Console.ReadLine()
Console.WriteLine("write the second number please")
dev4 = Console.ReadLine
Console.WriteLine("le resultat est : " & dev4 + dev3)
Console.WriteLine()
Console.WriteLine("appuyer sur stop pour terminer le programme")
dev5 = Console.ReadLine
If dev5 = "Stop" Then
Stop
End If
'la deuxiemle parti du prog qui permet de multiplier
ElseIf dev1 = "Multi" Then
Console.WriteLine("you choose " & dev1)
Console.WriteLine("write the first number please")
dev6 = Console.ReadLine()
Console.WriteLine("write the second number please")
dev7 = Console.ReadLine
Console.WriteLine("le resultat est : " & dev4 * dev3)
Console.WriteLine()
Console.WriteLine("appuyer sur stop pour terminer le programme")
dev8 = Console.ReadLine
If dev8 = "Stop" Then
Stop
End If
End If




End Sub

End Module
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