VB三种基本结构

VB中最经典的东西是什么？没错就是三种基本结构，顺序结构选择结构、、循环结构。

1、顺序结构

程序代码按照重上到下的顺序一行一行的执行，执行过程找那个没有分支，没有重复。

'输入a b
'交换a b 的值
Dim a As Integer
Dim b As Integer
a = Val(InputBox("a"))
b = Val(InputBox("b"))
c = a
a = b
b = c
MsgBox ("交换后a=" & a & "b=" & b)

2、选择结构

根据不同的条件判断来决定程序执行走向。



a)单分支结构 

'当a大于1时  显示a
If a > 1 Then
Print a
End If

b)双分支结构

'比较X,Y两个值中较大的一个

If x > Y Then
Print x
Else
Print Y
End If

c)多分支结构

'按成绩等级分类
If x >= 90 Then
Print "优秀"
ElseIf x >= 80 Then
Print "良好"
ElseIf x >= 70 Then
Print ""
ElseIf x >= 60 Then
Print ""
Else
Print ""
End If

d)情况语句

3、循环结构

根据条件判断某些语句可能需要执行0次1次或多次。

1)当型循环



'循环次数
Dim I As Long, S As Long
For I = 1 To 100
S = S + I
Next
MsgBox "For...Next：1+2+3+...+100 = " & S

Dim I As Long, S As Long
I = 0: S = 0
Do While I < 100
I = I + 1
S = S + I
Loop
MsgBox "Do While：1+2+3+...+100 = " & S

Dim I As Long, S As Long
I = 0: S = 0
Do Until I > 100
S = S + I
I = I + 1
Loop
MsgBox "Do Until：1+2+3+...+100 = " & S

Dim I As Long, S As Long
I = 0: S = 0
While I < 100
I = I + 1
S = S + I
Wend
MsgBox "While...Wend：1+2+3+...+100 = " & S

2)直到型循环

Dim I As Long, S As Long
I = 0: S = 0
Do
I = I + 1
If I > 100 Then Exit Do
S = S + I
Loop
MsgBox "Do...Loop：1+2+3+...+100 = " & S

Dim I As Long, S As Long
I = 0: S = 0
Do
I = I + 1
S = S + I
Loop While I < 100
MsgBox "Loop While：1+2+3+...+100 = " & S

Dim I As Long, S As Long
I = 0: S = 0
Do
S = S + I
I = I + 1
Loop Until I > 100
MsgBox "Loop Until：1+2+3+...+100 = " & S