Difference between revisions of "ZH/Documentation/BASIC Guide/Branching"
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Revision as of 22:06, 12 December 2008
可以使用分支语句限制代码块的执行,直到满足某个特定条件。
If...Then...Else
最常用的分支语句是 If 语句,如以下示例所示:
If A > 3 Then B = 2 End If
只有当变量 A 的值大于三时,才会进行 B = 2 赋值。If/Else 子句是 If 语句的变体:
If A > 3 Then B = 2 Else B = 0 End If
在该示例中,当 A 大于 3 时,则将 2 赋值给变量 B,否则,将 0 赋值给 B。
要使用更复杂的语句,您可以级联 If 语句,例如:
If A = 0 Then B = 0 ElseIf A < 3 Then B = 1 Else B = 2 End If
如果变量 A 的值等于零,则将 0 赋值给 B。如果 A 小于 3(但不等于零),则将 1 赋值给 B。在所有其他情况下(即 A 大于或等于 3),则将 2 赋值给 B。
Select...Case
Select...Case 指令可替代级联的 If 语句,它适用于需要根据各种条件来检查某个值的情况:
Select Case DayOfWeek Case 1: NameOfWeekday = "Sunday" Case 2: NameOfWeekday = "Monday" Case 3: NameOfWeekday = "Tuesday" Case 4: NameOfWeekday = "Wednesday" Case 5: NameOfWeekday = "Thursday" Case 6: NameOfWeekday = "Friday" Case 7: NameOfWeekday = "Saturday" End Select
在该示例中,工作日名称对应于一个数字,因此,对于 Sunday,将 1 赋值给 DayOfWeek 变量;对于 Monday 值,将 2 赋值给该变量,依此类推。
Select 命令并不限于简单的 1:1 赋值,您还可以在 Case 分支中指定比较运算符或表达式列表。以下示例列出了最重要的语法变体:
Select Case Var Case 1 To 5 ' ... Var is between the numbers 1 and 5 Case 6, 7, 8 ' ... Var is 6, 7 or 8 Case Var > 8 And Var < 11 ' ... Var is greater than 8 and less than 11 Case Else ' ... all other instances End Select
Content on this page is licensed under the Public Documentation License (PDL). |