Check if a string variable has an integer value

问题

I am working on a project which allows kids to send a message to Santa. Unfortunately, if they enter a string instead of an integer in the AGE field, the program crashes and returns Conversion from string "[exampleString]" to type 'Double' is not valid. Is there any way to check if they have entered an integer or not? This is the code.

If childAge > 0 And childAge < 150 Then
    fmSecA2 = "Wow! You are already " & childAge & " years old? You're growing to be a big " & childGender & " now! "
Else
    fmSecA2 = "Erm, I couldn't really understand your age. Are you making this up? Ho ho ho!"
End If

Thanks, Kai :)

回答1:

A very simple trick is to try parse the string as an Integer. If it succeeds, it is an integer (surprise surprise).

Dim childAgeAsInt As Integer
If Integer.TryParse(childAge, childAgeAsInt) Then
    ' childAge successfully parsed as Integer
Else
    ' childAge is not an Integer
End If

回答2:

You could perform the following two tests to be reasonably certain that the input you're getting is an integer:

If IsNumeric(childAge) AndAlso (InStr(1, childAge, ".") <> 0) Then
    fmSecA2 = "Wow! You are already " & childAge & " years old? You're growing to be a big " & childGender & " now! "
    If childAge < 0 OrElse childAge > 150 Then
        fmSecA2 = "I don't believe it's possible to be" & childAge & " years old..."
    End If
Else
    fmSecA2 = "Erm, I couldn't really understand your age. Are you making this up? Ho ho ho!"

The InStr function returns zero if it doesn't find the string that is being looked for, and so when combining that test with IsNumeric, you also rule out the possibility that some floating point data type was entered.

回答3:

Complementing Styxxy's response, if you dont need a result just replace it by vbNull:

If Integer.TryParse(childAge, vbNull) Then

回答4:

IsNumeric is built into VB, and will return a true/false

If IsNumeric(childAge) AndAlso (childAge > 0 And childAge < 150) Then
    fmSecA2 = "Wow! You are already " & childAge & " years old? You're growing to be a big " & childGender & " now! "
Else
    fmSecA2 = "Erm, I couldn't really understand your age. Are you making this up? Ho ho ho!"
End If

回答5:

You can use this.

Sub checkInt() 
    If IsNumeric(Range("A1")) And Not IsEmpty(Range("A1")) Then 

        If Round(Range("A1"), 0) / 1 = Range("A1") Then 
            MsgBox "Integer: " & Range("A1") 
        Else 
            MsgBox "Not Integer: " & Range("A1") 
        End If 
    Else 
        MsgBox "Not numeric or empty" 
    End If 
End Sub

回答6:

Working from Styxxy's answer, if you parse as a byte rather than an integer, then it also checks negative ages and maximum age of 255 all in one go.

Dim childAgeAsByte As Byte
If Byte.TryParse(childAge, childAgeAsByte) Then
    ' childAge successfully parsed as Byte
Else
    ' childAge is not a Byte
End If

Kristian

回答7:

Dim Input 

 Input = TextBox1.Text
 If Input > 0 Then 
   ............................
   ............................
 Else 
   TextBox2.Text = "Please only enter positive integers"
 End If

回答8:

In .Net you may use GetType() to determine the data type of a variable.

Dim n1 As Integer = 12
Dim n2 As Integer = 82
Dim n3 As Long = 12

Console.WriteLine("n1 and n2 are the same type: {0}",
                  Object.ReferenceEquals(n1.GetType(), n2.GetType()))
Console.WriteLine("n1 and n3 are the same type: {0}",
                  Object.ReferenceEquals(n1.GetType(), n3.GetType()))
' The example displays the following output: 
'       n1 and n2 are the same type: True 
'       n1 and n3 are the same type: False

Based on the above sample you can write a code snippet:

If childAge.GetType() = "Integer" then '-- also use childAge.GetType().Name = "Int32"
  ' do something
End if

Reference MSDN

来源：https://stackoverflow.com/questions/13980538/check-if-a-string-variable-has-an-integer-value

标签

vb.net

string

visual-studio-2010

parsing

integer