找素数，十六进制转十进制（正解）

'判断一个整数是否是素数(Prime)

Function isPrime(n%) As Boolean
    Dim f As Boolean = true
    Dim i%
    For i = 2 To n/2
        If n Mod i = 0 Then f = False : Exit For
    Next
    Return f
End Function

'举例

Dim n%
For i = 800 To 900
    If isPrime(i) Then n += 1 : Label1.Text &= i & VbCrLf
Next
Msgbox(n)

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’十六进制转十进制

Dim s, c As String
Dim n, h As Integer

s = UCase(TextBox1.Text)
n = Len(s)
For i = 1 To n
    c = Mid(s, i ,1)
    If c >= "0" And c <= "9" Then
        h = h* 16 + Val(c)
    Elseif c >= "A"
        h = h * 16 + Asc(c) - 55

'以a5b为例
'十六进制中a=10 : b = 11

h=10
h=10*16 + 5
h=(10 * 16 + 5)*16 + 11

'即h = 10 * 16 * 16 + 5 * 16  + 11
'即h = 10 * ( 16 ^ 2 ) + 5 * ( 16 ^ 1 ) + 11 * ( 16 ^ 0 )


------------------------------------下面是一些零碎的课堂笔记

'求大数原来是有个函数的吗

Max = IIf(x > y, x, y)

'If语句中的表达式
可以是关系表达式、逻辑表达式或算术表达式