vb.net 控制台应用程序质数
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Console application prime number
提问by Stan Harris
I'm supposed to create a form program and a console program to determine prime numbers. I've completed the form program but i'm having trouble with the Console program.
我应该创建一个表单程序和一个控制台程序来确定素数。我已经完成了表单程序，但我在使用控制台程序时遇到了问题。
I feel i almost got it working, the only thing is sometimes it only works every second input, and sometimes errors still crash the program even though i have an On Error statement.
我觉得我几乎让它工作了，唯一的问题是有时它只能在每秒输入一次，有时即使我有一个 On Error 语句，错误仍然会使程序崩溃。
If anyone can explain to me why this is happening I would be grateful. I want to understand why it's doing what it's doing. Should I maybe use a Case Statement rather than a Do Loop?
如果有人能向我解释为什么会发生这种情况，我将不胜感激。我想了解它为什么要做它正在做的事情。我应该使用 Case 语句而不是 Do 循环吗？
Current Code:
当前代码：
Module Module1
Sub Main()
System.Console.WriteLine("Enter a number from 1 to 10000 to find out if it's prime, Type END to exit")
ExitHere:
Do
On Error GoTo ErrorHandler
Dim UserInput As Integer = Integer.Parse(Console.ReadLine())
Dim IsItPrime As Boolean = False
Dim i As Integer
For i = 2 To (UserInput - 1)
If UserInput Mod i = 0 Then
IsItPrime = False
Exit For
End If
Next i
If i = UserInput Then
System.Console.WriteLine(UserInput & " is a Prime Number.")
Else
System.Console.WriteLine(UserInput & " is not a prime number.")
End If
Loop Until Console.ReadLine = "End"
Exit Sub
ErrorHandler:
Console.WriteLine("There seems to have been an error.")
GoTo ExitHere
End Sub
End Module
回答by Idle_Mind
I'd write it something more like:
我会写一些更像：
Sub Main()
Dim response As String
Do
Console.Write("Enter an integer from 1 to 10000, or `END` to exit: ")
response = Console.ReadLine().ToUpper
If response <> "END" Then
Dim UserInput As Integer
If Integer.TryParse(response, UserInput) Then
If UserInput >= 1 AndAlso UserInput <= 10000 Then
Dim IsItPrime As Boolean = True ' assume it's prime until proven otherwise
If UserInput > 3 Then
For i As Integer = 2 To (UserInput - 1)
If UserInput Mod i = 0 Then
IsItPrime = False
Exit For
End If
Next i
End If
If IsItPrime Then
System.Console.WriteLine(UserInput & " is a Prime Number.")
Else
System.Console.WriteLine(UserInput & " is NOT a prime number.")
End If
Else
Console.WriteLine("Out of Valid Range")
End If
Else
Console.WriteLine("Invalid Integer.")
End If
End If
Loop While response <> "END"
End Sub
回答by the_lotus
You have two ReadLine, you should only have one. Remove the ReadLine inside the Loop Until. Store the value of the first ReadLine and determine if it's a number or End.
你有两个 ReadLine，你应该只有一个。删除循环直到内的 ReadLine。存储第一个 ReadLine 的值并确定它是数字还是 End。
Dim input As String = Console.ReadLine()
Dim inputNumber As Integer
If input = "End" Then
Exit Do
Else If Integer.TryParse(input, inputNumber) Then
' It's a number
Else
' Invalid input
End If
回答by KUDUS
Sub Main()
Dim n As Integer = 1
Dim counter As Integer
Dim x As Integer
Console.Write("Enter A Number : ")
x = Console.ReadLine
While n <= x
If x Mod n = 0 Then
counter = counter + 1
End If
n = n + 1
End While
If counter <= 2 Then
Console.WriteLine("This Number is a Prime")
Else
Console.WriteLine("This Number is a Composite")
End If
Console.ReadLine()
End Sub
