How to check if an object is numeric in C#

Question

I'm trying to check if an object is a number or not.

The IsNumeric function below works most of the time except when I pass a value of "NaN"

So I have this:

    private void button1_Click(object sender, EventArgs e)
    {
        object obj = "NaN";

        bool check = IsNumeric(obj);

        if (check)
        {
            MessageBox.Show(obj.ToString() + " is a number");
        }


    }

    public bool IsNumeric(object Expression)
    {
        bool isNum;
        double retNum;
        isNum = Double.TryParse(Convert.ToString(Expression), out retNum);
        return isNum;
    }

But the IsNumeric funciton returns "true" which is a lie.

I found the suggestion of the IsNumeric function here: How do I identify if a string is a number?

How can I check if an object is numeric or not?

https://msdn.microsoft.com/en-us/library/system.object.gettype%28v=vs.110%29.aspx `Object.GetType()` it is a thing in C# — MethodMan, Feb 05 '15 at 22:16
if he wanted to check string value then why is there a `IsNumeric` wow @NadiaChibrikova can you elaborate — MethodMan, Feb 05 '15 at 22:18
Do you expect "NaN" _not_ to be recognized as a number? You could easily exclude that using an `if()` statement. — CodeCaster, Feb 05 '15 at 22:21
@Pabinator, I'm confused as to whether you have an object of unknown type that you want to check (as your description suggests), or if you have a string value that you want to check (as your code suggests). — Katie Kilian, Feb 05 '15 at 22:21
There are some great solutions to this problem here: http://stackoverflow.com/questions/1130698/checking-if-an-object-is-a-number-in-c-sharp — Icemanind, Feb 05 '15 at 22:24
@NadiaChibrikova try my example and put "123" it will still be a type of System.String vs 123 will be of type System.Int32 — MethodMan, Feb 05 '15 at 22:27
@MethodMan I know that, but I think he wants to consider "123" as numeric — Nadia Chibrikova, Feb 05 '15 at 22:29
doesn't matter - the code speaks for it's self.. and if `IsNumeric Function is used properly it wouldn't be an issue either.. — MethodMan, Feb 05 '15 at 22:30
other examples as well can be found here -http://stackoverflow.com/questions/1130698/checking-if-an-object-is-a-number-in-c-sharp — MethodMan, Feb 05 '15 at 22:30
also why not use the var as a string instead of `object` and it will be much easier to accurately determine if the string is a string or integer I will post an even simpler method.. — MethodMan, Feb 05 '15 at 22:49
Are any of these numbers: "seven", "pi", "XLII", "0xDeadBeef", "GDP of the UK in 1993", "sqrt(-1)", "i", "e", "6.02e23", "2^128", "1 megaton TNT in grams of mass defect", "answer to the ultimate question of life, the universe, and everything"? Perhaps there's a [WolframAlpha](http://www.wolframalpha.com/) API that would help. — HABO, Feb 05 '15 at 22:50

score 2 · Answer 1 · answered Feb 05 '15 at 22:18

2

If you don't mind adding a reference to the VB library you can use:

Microsoft.VisualBasic.Information.IsNumeric(expression)

answered Feb 05 '15 at 22:18

D Stanley

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Nadia Chibrikova · Accepted Answer · 2015-02-05T22:54:02.737

1

If your only trouble is with "NaN" then try this: isNum = Double.TryParse(Convert.ToString(Expression), out retNum) && !Double.IsNaN(retNum);

Btw "Infinity" and "-Infinity" also will be numeric.

edited Feb 05 '15 at 22:54

answered Feb 05 '15 at 22:34

Nadia Chibrikova

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How to check if an object is numeric in C#

2 Answers2