回文字符串的特征是从左到右读和从右到左读是完全一样的,如“aba”、“aabbaa”,判断字符串中忽略“,”字符后,该字符串是否是回文字符串的VB程序段如下:
s = "ab,,,cb,a"
n = Len(s)
i = 1: j = Len(s)
flag = True
Do While i <= j
If Mid(s, i, 1) = Mid(s, j, 1) Then
i = i + 1: j = j - 1
Else
End If
Loop
If flag = False Then Print ("不是回文") Else Print ("回文")
方框中的代码由以下三部分组成:
① If Mid(s, i, 1) = "," Or Mid(s, i, 1) = "." Then i = i + 1
② If Mid(s, j, 1) = "," Or Mid(s, j, 1) = "." Then j = j – 1
③ If Mid(s, i, 1) <> "," And Mid(s, j, 1) <> "," Then flag = False: Exit Do
下列选项中,代码顺序正确的是:( )