What is the C# equivalent of NaN or IsNumeric?

Question

What is the most efficient way of testing an input string whether it contains a numeric value (or conversely Not A Number)? I guess I can use Double.Parse or a

Answer 1

Actually, Double.NaN is supported in all .NET versions 2.0 and greater.

Answer 2

I know this has been answered in many different ways, with extensions and lambda examples, but a combination of both for the simplest solution.

public static bool IsNumeric(this String s)
{
    return s.All(Char.IsDigit);
}

or if you are using Visual Studio 2015 (C# 6.0 or greater) then

public static bool IsNumeric(this String s) => s.All(Char.IsDigit);

Awesome C#6 on one line. Of course this is limited because it just tests for only numeric characters.

To use, just have a string and call the method on it, such as:

bool IsaNumber = "123456".IsNumeric();

Answer 3

This is a modified version of the solution proposed by Mr Siir. I find that adding an extension method is the best solution for reuse and simplicity in the calling method.

public static bool IsNumeric(this String s)
{
    try { double.Parse(s); return true; }
    catch (Exception) { return false; }
}

I modified the method body to fit on 2 lines and removed the unnecessary .ToString() implementation. For those not familiar with extension methods here is how to implement:

Create a class file called ExtensionMethods. Paste in this code:

using System;
using System.Collections.Generic;
using System.Text;

namespace YourNameSpaceHere
{
    public static class ExtensionMethods
    {
        public static bool IsNumeric(this String s)
        {
            try { double.Parse(s); return true; }
            catch (Exception) { return false; }
        }
    }
}

Replace YourNameSpaceHere with your actual NameSpace. Save changes. Now you can use the extension method anywhere in your app:

bool validInput = stringVariable.IsNumeric();

Note: this method will return true for integers and decimals, but will return false if the string contains a comma. If you want to accept input with commas or symbols like "$" I would suggest implementing a method to remove those characters first then test if IsNumeric.