"這題目對初學者，其實很有難度，執行效果如下

Private Sub command1_click()

Dim X As String

Dim brr

Dim a As Long

Dim b As Long

Dim c As Long

X = InputBox("請輸入3個整數(以英文逗號分隔)：", "求最大數", "例如：3,344,51", 1000, 1000)

brr = Split(X, ",")

If UBound(brr) > 2 Then

MsgBox "輸入數字多餘3個，請重新輸入！", , "提醒"

End "退出

End If

If UBound(brr)

MsgBox "輸入數字少餘3個，請重新輸入！", , "提醒"

End "退出

End If

a = brr(0)

b = brr(1)

c = brr(2)

MsgBox "這三個數的最大數是" & Max(Max(a, b), c), , "最大數顯示"

End Sub

Function Max(n1 As Long, n2 As Long) As Long

Max = IIf(n1 > n2, n1, n2)

End Function