Microsoft Visual Basic 2010(более ранние тоже прокатят)
Dim I As Single
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
I = Val(InputBox("Введите число"))
If I >= 0 Then
I = I - 50
Else
I = I + 100
End If
MsgBox(I)
End Sub
Просто на Basic
Dim I As Single
Input(I)
If I >= 0 Then
I = I - 50
Else
I = I + 100
End If
Print I
End