Is there a better way to test for an integer in C# than Double.TryParse?

Question

Double.TryParse returns a value, and I don't need a value. I need to be able to tell if a string is numeric and just return a bool.

is there a way to do this?

Answer 1

One way is to add a reference to Microsoft.VisualBasic and then use Information.IsNumeric().

using Microsoft.VisualBasic;

...

if (Information.IsNumeric("1233434.0"))
{
    Console.WriteLine("Yes");
}

Answer 2

Well, you could use a regular expression, but why not just discard the value from Double.TryParse and move on? I don't think it will be worth the effort trying to duplicate this code.

Answer 3

How about a regular expression?

string s = "13.2";
bool bIsDecimal = Regex.IsMatch("^-?\d+(\.\d+)?$");

should test whether it is a decimal value. What it won't tell you is whether it is a valid decimal, as in, will the number fit in the range of a decimal.

Answer 4

I would consider exactly what you need to determine. "Is numeric" is vaguer than it sounds at first. Consider the following strings, and whether you'd want to consider them numeric:

• "NaN"
• "Nan"
• "Infinity"
• "0.000000000000000000000000000000000000000000000000001"
• "1e5"
• "1e500"
• "1,000"
• "+1"

Using Double.TryParse (with an en-GB culture - don't forget about cultural issues!) will give you True, False, True, True (despite it not being representable), True, False. True, True.

If you want to tell whether a later call to Double.TryParse would succeed, calling it here will be the most accurate solution. If you're using some other criteria, a regular expression may well be more appropriate. An example of the criteria you might use:

• The can be a + or -, but only in the first character
• There can be a single period at any character. You may want to avoid one at the end - should "1." be valid?
• Other than the above, all characters must be digits

That would disallow all but the fourth and last examples above.

EDIT: I've now noticed the title of the question includes "integer". That pretty much reduces the specification checks to:

• Do you want to allow leading zeroes (e.g. -00012)?
• What is the range?
• Do you only need decimals (instead of hex etc)?
• Do you need to accept thousands separators?
• What's your policy on leading/trailing whitespace?

Answer 5

I just fired up Visual Studio Express (both 2005 and 2008). The Intellisense says that the return value of Double.TryParse() is a bool. The following worked for me under limited testing...

double res; // you must be under very resource-constrained 
            // conditions if you can't just declare a double
            // and forget about it

if (Double.TryParse(textBox1.Text, out res)) {
    label1.Text = "it's a number";
} else {
    label1.Text = "not a number";
}

Answer 6

Hi,

try this isnumeric:

public static bool IsNumeric(object Expression)

{

  bool isNum;

  double retNum;

  isNum = Double.TryParse(Convert.ToString(Expression), System.Globalization.NumberStyles.Any,System.Globalization.NumberFormatInfo.InvariantInfo, out retNum );

  return isNum;

}