vb-4-循环结构程序设计教学内容.ppt

第4章 循环结构程序设计
第六次课
本章内容
循环结构
用For-Next语句实现循环结构
用Do While-Loop语句实现循环结构
嵌套的循环结构
循环结构
ac = Fac * i
Next i
= Fac
End Sub
1！+2！+3！+……+15!
Private Sub cmdCal_Click()
Dim Fac As long, sum As long
Dim i As Integer
Fac=1
For i = 1 To 15
Fac = Fac * i
sum=sum+Fac
Next i
= sum
End Sub
分析程序运行结果
i=1 fac=1*1 sum=1
i=2 fac=1*2 sum=1+2
i=3 fac=1*2*3=3！
sum=1!+2!+3!
i=4 fac=1*2*3*4=4!
sum=1+2+3!+4!
i=5 fac=4!*5=5!
sum=1+2!+3!+4!+5!
………………
用While语句实现循环
语句形式：
While 条件
[循环体]
Wend
语句说明：
“条件”一般为条件表达式，结果为布尔变量True或False。
“条件”用于控制“循环体”是否执行。
多用于循环次数不定的情况。
用While语句实现循环
语句执行过程：

“计算”按钮完整代码:
Private Sub cmdcal_Click()
Dim i As Integer
Dim sum As Long, n As Long
n = Val()
For i = 1 To n
sum = sum + i
Next i
= sum
End Sub
i = 1
While i <= ｎ
sum = sum + i
i = i + 1
wend
用While语句实现循环
【】实现1*2*3*……*n的操作，当阶乘值>5000时结束操作。
txtcyc
txtfac
代码编写
Private Sub cmdcal_Click()
Dim i As Integer，fac As Long
i = 1:fac = 1
While fac <= 5000
fac = fac * i
i = i + 1
= i
= fac
Wend
End Sub
初始化语句是否可以去掉？
代码编写
“手动计算”按钮：单步演示累乘结果，需要窗体级变量保留成绩，及点击次数
Private Sub Cmdcalh_Click()
If j = 0 Then fact = 1
If fact <= 5000 Then
j = j + 1
fact = fact * j
= j
= fact
Else
= False
End If
End Sub
该语句的作用？
用DO语句实现循环
Do While – Loop语句
Do While 条件
循环体语句
Loop
Do – Loop While语句
Do
循环体语句
Loop While 条件
先执行，后判断至少执行一次循环体
先判断，后执行有可能一次也不执行
用DO语句实现循环
用Do While – Loop
“计算”按钮完整代码:
Private Sub cmdcal_Click()
Dim i As Integer
Dim sum As Long, n As Long
n = Val()
For i = 1 To n
sum = sum + i
Next i
= sum
End Sub
i = 1
Do While i <= ｎ
sum = sum + i
i = i + 1
Loop
执行过程
No
Yes
sum = sum + i
i <= 100
i = i + 1
用Do – Loop While语句改写