Is this string numeric?

[KoRUPT]

Is there a function that checks strings for only numbers? psuedo code example:

//I know that these namespaces dont exist.. just giving you an idea of what I want
System.IsNumeric("88338k33" //returns false
System.IsNumeric("9303 39" //returns false
System.IsNumeric("929229" //returns true

I saw something like this for characters but not for strings.

Thanks.

 

[Craig0201]

Straight from help....

Public Function IsNumeric(ByVal Expression As Object) As Boolean
Parameter
Expression
Required. Object expression.
Remarks
IsNumeric returns True if the entire Expression is recognized as a number; otherwise, it returns False.

IsNumeric returns True if the data type of Expression is Short, Integer, Long, Decimal, Single, or Short. It also returns True if Expression is a String that can be successfully converted to a Double. It returns False if Expression is of data type Date.

Example
This example uses the IsNumeric function to determine if the contents of a variable can be evaluated as a number.

Dim MyVar As Object
Dim MyCheck As Boolean
' ...
MyVar = "53" ' Assign value.
MyCheck = IsNumeric(MyVar) ' Returns True.
' ...
MyVar = "459.95" ' Assign value.
MyCheck = IsNumeric(MyVar) ' Returns True.
' ...
MyVar = "45 Help" ' Assign value.
MyCheck = IsNumeric(MyVar) ' Returns False.

Craig

 

[KoRUPT]

That would help me A LOT, if I was posting in a VB forum

Anyone have an C# solutions?

Thanks

 

[Alcar]

[translated to c#]
object MyVar;
boolean MyCheck;

// ...
MyVar = "53"; // Assign value.
MyCheck = IsNumeric(MyVar); // Returns True.
// ...
MyVar = "459.95"; // Assign value.
MyCheck = IsNumeric(MyVar); // Returns True.
// ...
MyVar = "45 Help"; // Assign value.
MyCheck = IsNumeric(MyVar); // Returns False.

[author Craig]

 

[KoRUPT]

That does not work either. If someone could tell me which namespace the IsNumeric() function is in, then it should work.

Thank you.

 

[Alcar]

sorry my fault. In c# it's IsNumber. Here is the example

using System;

public class IsNumberSample {
public static void Main() {
string str = "non-numeric";

Console.WriteLine(Char.IsNumber('8')); // Output: "True"
Console.WriteLine(Char.IsNumber(str, 3)); // Output: "False"
}
}

 

[KoRUPT]

Hmmm... so I guess the only way is to do it a character at a time. Thanks for your help. I'll do it this way.

 

[chiph]

KoRUPT -

The 2nd overload for the IsNumber function accepts a string, so no need to do it a character at a time. Take a look at:

ms-help://MS.VSCC/MS.MSDNVS/cpref/html/frlrfSystemCharClassIsNumberTopic.htm

Chip H.

 

[KoRUPT]

Yes it does accept a string. It also accepts an integer specifying the character to check. So you DO have to do it a character at a time;

From the Help:
Indicates whether the character at the specified position in a specified string is categorized as a decimal digit or hexadecimal number.

[C#] public static bool IsNumber(string, int);


Example:
using System;

public class IsNumberSample {
public static void Main() {
string str = "889n999";
Console.WriteLine(Char.IsNumber('8')); //Output: "True"
Console.WriteLine(Char.IsNumber(str, 3)); //Output: "False"
Console.WriteLine(Char.IsNumber(str, 2)); //Output: "True"
}
}

 

[chiph]

Uh-Oh. You're right.
Character at a time it is.

Maybe you could wrapper it in a static method to make it easier to use.

Chip H.

 

[Larsson]

That check is not so difficult to do.
This function will return true if the string only has numbers.

private bool CheckForNumeric(string s)
{
bool onlynumber = false;

for (int i=0; i<s.Length; i++)
{
int keyInt = (int)s;
//Only numbers between 48 and 57.
if ( keyInt < 48 || keyInt > 57)
onlynumber = true;
else
return false;
}
return onlynumber;
}

CheckForNumeric(&quot;4567&quot; returns true;
CheckForNumeric(&quot;45j345&quot; returns false;

Larsson

 

[Guest_imported]

A method that I've been using is to try and convert it to a number using the System.Int32.Parse() method. If it isn't a number, it will throw an exception which you can catch and return a false instead.

AS

 

[GoatNat]

Using int32.Parse() and catching the exception contains way too much overhead. On operations in which it passes it will be quick, on failures you're going to take a performance hit..

I did two tests, one with an int.Parse() catching the exception and another in which i turned the string into a char array and looped over each character and did char.IsNumeric() (see code below).. i did each 40,000 times with 3 failures and 1 pass, the resulting int.parse took 37 seconds to complete all 40,000 operations, the 2nd solution took 0.02 seconds. These of course are extreme situations but gives you a good idea on what to expect under increased load.

private static bool IsNumeric(string Source)
{
try
{
int.Parse(Source);
return true;
}
catch(Exception)
{
return false;
}
}

private static bool IsNumeric2(string Source)
{
foreach(char CurrentCharacter in Source.ToCharArray())
{
if (!char.IsNumber(CurrentCharacter))
return false;
}

return true;
}

 

[mhauser]

You can also do this using a regular expression. This would allow you to check for a specific kind of number:
Integer, Decimal, Negative/Non-Negative.

Regular expressions are very powerful for evaluating strings.

http://www.evolt.org/article/rating/20/22700/

http://www.regxlib.com/

http://www.regxlib.com/RETester.aspx

here is some example code:

using System.Text.RegularExpressions;

bool valid = true;

string regExp = GetRegExp(); // Build your expression
if ( !Regex.IsMatch(this.Text, regExp ) )
valid = false;

return valid;