Do
a = Val(InputBox("請輸入長方形的長度"))
If a <= 0 Then MsgBox "長方形的長度必須大於0,請重新輸入!"
Loop While a <= 0
b = Val(Inputbox("請輸入長方形的寬度"))
If b <= 0 Then MsgBox "長方形的寬度必須大於0,請重新輸入!"
Loop While b <= 0
MsgBox "長" & a & "寬" & b & "的長方形,面積是" & (a * b)