Identify if a string is a number

Question

If I have these strings:

1. "abc" = false

2. "123" = true

3. "ab2" = false

Is there a command, like IsNumeric() or something else, that can identify if a string is a valid number?

Answer 1

int n;
bool isNumeric = int.TryParse("123", out n);

Update As of C# 7:

var isNumeric = int.TryParse("123", out int n);

or if you don't need the number you can discard the out parameter

var isNumeric = int.TryParse("123", out _);

The var s can be replaced by their respective types!

Answer 2

This will return true if input is all numbers. Don't know if it's any better than TryParse, but it will work.

Regex.IsMatch(input, @"^\d+$")

If you just want to know if it has one or more numbers mixed in with characters, leave off the ^ + and $.

Regex.IsMatch(input, @"\d")

Edit: Actually I think it is better than TryParse because a very long string could potentially overflow TryParse.

Answer 3

You can also use:

stringTest.All(char.IsDigit);

It will return true for all Numeric Digits (not float) and false if input string is any sort of alphanumeric.

Please note: stringTest should not be an empty string as this would pass the test of being numeric.

Answer 4

I've used this function several times:

public static bool IsNumeric(object Expression)
{
    double retNum;

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

But you can also use;

bool b1 = Microsoft.VisualBasic.Information.IsNumeric("1"); //true
bool b2 = Microsoft.VisualBasic.Information.IsNumeric("1aa"); // false

From Benchmarking IsNumeric Options

_{(source: aspalliance.com)}

_{(source: aspalliance.com)}

Answer 5

This is probably the best option in C#.

If you want to know if the string contains a whole number (integer):

string someString;
// ...
int myInt;
bool isNumerical = int.TryParse(someString, out myInt);

The TryParse method will try to convert the string to a number (integer) and if it succeeds it will return true and place the corresponding number in myInt. If it can't, it returns false.

Solutions using the int.Parse(someString) alternative shown in other responses works, but it is much slower because throwing exceptions is very expensive. TryParse(...) was added to the C# language in version 2, and until then you didn't have a choice. Now you do: you should therefore avoid the Parse() alternative.

If you want to accept decimal numbers, the decimal class also has a .TryParse(...) method. Replace int with decimal in the above discussion, and the same principles apply.

Answer 6

You can always use the built in TryParse methods for many datatypes to see if the string in question will pass.

Example.

decimal myDec;
var Result = decimal.TryParse("123", out myDec);

Result would then = True

decimal myDec;
var Result = decimal.TryParse("abc", out myDec);

Result would then = False

Answer 7

In case you don't want to use int.Parse or double.Parse, you can roll your own with something like this:

public static class Extensions
{
    public static bool IsNumeric(this string s)
    {
        foreach (char c in s)
        {
            if (!char.IsDigit(c) && c != '.')
            {
                return false;
            }
        }

        return true;
    }
}

Answer 8

If you want to catch a broader spectrum of numbers, à la PHP's is_numeric, you can use the following:

// From PHP documentation for is_numeric
// (http://php.net/manual/en/function.is-numeric.php)

// Finds whether the given variable is numeric.

// Numeric strings consist of optional sign, any number of digits, optional decimal part and optional
// exponential part. Thus +0123.45e6 is a valid numeric value.

// Hexadecimal (e.g. 0xf4c3b00c), Binary (e.g. 0b10100111001), Octal (e.g. 0777) notation is allowed too but
// only without sign, decimal and exponential part.
static readonly Regex _isNumericRegex =
    new Regex(  "^(" +
                /*Hex*/ @"0x[0-9a-f]+"  + "|" +
                /*Bin*/ @"0b[01]+"      + "|" + 
                /*Oct*/ @"0[0-7]*"      + "|" +
                /*Dec*/ @"((?!0)|[-+]|(?=0+\.))(\d*\.)?\d+(e\d+)?" + 
                ")$" );
static bool IsNumeric( string value )
{
    return _isNumericRegex.IsMatch( value );
}

Unit Test:

static void IsNumericTest()
{
    string[] l_unitTests = new string[] { 
        "123",      /* TRUE */
        "abc",      /* FALSE */
        "12.3",     /* TRUE */
        "+12.3",    /* TRUE */
        "-12.3",    /* TRUE */
        "1.23e2",   /* TRUE */
        "-1e23",    /* TRUE */
        "1.2ef",    /* FALSE */
        "0x0",      /* TRUE */
        "0xfff",    /* TRUE */
        "0xf1f",    /* TRUE */
        "0xf1g",    /* FALSE */
        "0123",     /* TRUE */
        "0999",     /* FALSE (not octal) */
        "+0999",    /* TRUE (forced decimal) */
        "0b0101",   /* TRUE */
        "0b0102"    /* FALSE */
    };

    foreach ( string l_unitTest in l_unitTests )
        Console.WriteLine( l_unitTest + " => " + IsNumeric( l_unitTest ).ToString() );

    Console.ReadKey( true );
}

Keep in mind that just because a value is numeric doesn't mean it can be converted to a numeric type. For example, "999999999999999999999999999999.9999999999" is a perfeclty valid numeric value, but it won't fit into a .NET numeric type (not one defined in the standard library, that is).

Answer 9

I know this is an old thread, but none of the answers really did it for me - either inefficient, or not encapsulated for easy reuse. I also wanted to ensure it returned false if the string was empty or null. TryParse returns true in this case (an empty string does not cause an error when parsing as a number). So, here's my string extension method:

public static class Extensions
{
    /// <summary>
    /// Returns true if string is numeric and not empty or null or whitespace.
    /// Determines if string is numeric by parsing as Double
    /// </summary>
    /// <param name="str"></param>
    /// <param name="style">Optional style - defaults to NumberStyles.Number (leading and trailing whitespace, leading and trailing sign, decimal point and thousands separator) </param>
    /// <param name="culture">Optional CultureInfo - defaults to InvariantCulture</param>
    /// <returns></returns>
    public static bool IsNumeric(this string str, NumberStyles style = NumberStyles.Number,
        CultureInfo culture = null)
    {
        double num;
        if (culture == null) culture = CultureInfo.InvariantCulture;
        return Double.TryParse(str, style, culture, out num) && !String.IsNullOrWhiteSpace(str);
    }
}

Simple to use:

var mystring = "1234.56789";
var test = mystring.IsNumeric();

Or, if you want to test other types of number, you can specify the 'style'. So, to convert a number with an Exponent, you could use:

var mystring = "5.2453232E6";
var test = mystring.IsNumeric(style: NumberStyles.AllowExponent);

Or to test a potential Hex string, you could use:

var mystring = "0xF67AB2";
var test = mystring.IsNumeric(style: NumberStyles.HexNumber)

The optional 'culture' parameter can be used in much the same way.

It is limited by not being able to convert strings that are too big to be contained in a double, but that is a limited requirement and I think if you are working with numbers larger than this, then you'll probably need additional specialised number handling functions anyway.

Answer 10

UPDATE of Kunal Noel Answer

stringTest.All(char.IsDigit);
// This returns true if all characters of the string are digits.

But, for this case we have that empty strings will pass that test, so, you can:

if (!string.IsNullOrEmpty(stringTest) && stringTest.All(char.IsDigit)){
   // Do your logic here
}

Answer 11

You can use TryParse to determine if the string can be parsed into an integer.

int i;
bool bNum = int.TryParse(str, out i);

The boolean will tell you if it worked or not.

Answer 12

If you want to know if a string is a number, you could always try parsing it:

var numberString = "123";
int number;

int.TryParse(numberString , out number);

Note that TryParse returns a bool, which you can use to check if your parsing succeeded.

Answer 13

I guess this answer will just be lost in between all the other ones, but anyway, here goes.

I ended up on this question via Google because I wanted to check if a string was numeric so that I could just use double.Parse("123") instead of the TryParse() method.

Why? Because it's annoying to have to declare an out variable and check the result of TryParse() before you know if the parse failed or not. I want to use the ternary operator to check if the string is numerical and then just parse it in the first ternary expression or provide a default value in the second ternary expression.

Like this:

var doubleValue = IsNumeric(numberAsString) ? double.Parse(numberAsString) : 0;

It's just a lot cleaner than:

var doubleValue = 0;
if (double.TryParse(numberAsString, out doubleValue)) {
    //whatever you want to do with doubleValue
}

I made a couple extension methods for these cases:

---

Extension method one

public static bool IsParseableAs<TInput>(this string value) {
    var type = typeof(TInput);

    var tryParseMethod = type.GetMethod("TryParse", BindingFlags.Static | BindingFlags.Public, Type.DefaultBinder,
        new[] { typeof(string), type.MakeByRefType() }, null);
    if (tryParseMethod == null) return false;

    var arguments = new[] { value, Activator.CreateInstance(type) };
    return (bool) tryParseMethod.Invoke(null, arguments);
}

Example:

"123".IsParseableAs<double>() ? double.Parse(sNumber) : 0;

Because IsParseableAs() tries to parse the string as the appropriate type instead of just checking if the string is "numeric" it should be pretty safe. And you can even use it for non numeric types that have a TryParse() method, like DateTime.

The method uses reflection and you end up calling the TryParse() method twice which, of course, isn't as efficient, but not everything has to be fully optimized, sometimes convenience is just more important.

This method can also be used to easily parse a list of numeric strings into a list of double or some other type with a default value without having to catch any exceptions:

var sNumbers = new[] {"10", "20", "30"};
var dValues = sNumbers.Select(s => s.IsParseableAs<double>() ? double.Parse(s) : 0);

---

Extension method two

public static TOutput ParseAs<TOutput>(this string value, TOutput defaultValue) {
    var type = typeof(TOutput);

    var tryParseMethod = type.GetMethod("TryParse", BindingFlags.Static | BindingFlags.Public, Type.DefaultBinder,
        new[] { typeof(string), type.MakeByRefType() }, null);
    if (tryParseMethod == null) return defaultValue;

    var arguments = new object[] { value, null };
    return ((bool) tryParseMethod.Invoke(null, arguments)) ? (TOutput) arguments[1] : defaultValue;
}

This extension method lets you parse a string as any type that has a TryParse() method and it also lets you specify a default value to return if the conversion fails.

This is better than using the ternary operator with the extension method above as it only does the conversion once. It still uses reflection though...

Examples:

"123".ParseAs<int>(10);
"abc".ParseAs<int>(25);
"123,78".ParseAs<double>(10);
"abc".ParseAs<double>(107.4);
"2014-10-28".ParseAs<DateTime>(DateTime.MinValue);
"monday".ParseAs<DateTime>(DateTime.MinValue);

Outputs:

123
25
123,78
107,4
28.10.2014 00:00:00
01.01.0001 00:00:00

Answer 14

If you want to check if a string is a number (I'm assuming it's a string since if it's a number, duh, you know it's one).

• Without regex and
• using Microsoft's code as much as possible

you could also do:

public static bool IsNumber(this string aNumber)
{
     BigInteger temp_big_int;
     var is_number = BigInteger.TryParse(aNumber, out temp_big_int);
     return is_number;
}

This will take care of the usual nasties:

• Minus (-) or Plus (+) in the beginning
• contains decimal character BigIntegers won't parse numbers with decimal points. (So: BigInteger.Parse("3.3") will throw an exception, and TryParse for the same will return false)
• no funny non-digits
• covers cases where the number is bigger than the usual use of Double.TryParse

You'll have to add a reference to System.Numerics and have using System.Numerics; on top of your class (well, the second is a bonus I guess :)

Answer 15

Double.TryParse

bool Double.TryParse(string s, out double result)

Answer 16

The best flexible solution with .net built-in function called- char.IsDigit. It works with unlimited long numbers. It will only return true if each character is a numeric number. I used it lot of times with no issues and much easily cleaner solution I ever found. I made a example method.Its ready to use. In addition I added validation for null and empty input. So the method is now totally bulletproof

public static bool IsNumeric(string strNumber)
    {
        if (string.IsNullOrEmpty(strNumber))
        {
            return false;
        }
        else
        {
            int numberOfChar = strNumber.Count();
            if (numberOfChar > 0)
            {
                bool r = strNumber.All(char.IsDigit);
                return r;
            }
            else
            {
                return false;
            }
        }
    }

Answer 17

Try the reges below

new Regex(@"^\d{4}").IsMatch("6")    // false
new Regex(@"^\d{4}").IsMatch("68ab") // false
new Regex(@"^\d{4}").IsMatch("1111abcdefg")
new Regex(@"^\d+").IsMatch("6") // true (any length but at least one digit)

Answer 18

With c# 7 it you can inline the out variable:

if(int.TryParse(str, out int v))
{
}

Answer 19

Use these extension methods to clearly distinguish between a check if the string is numerical and if the string only contains 0-9 digits

public static class ExtensionMethods
{
    /// <summary>
    /// Returns true if string could represent a valid number, including decimals and local culture symbols
    /// </summary>
    public static bool IsNumeric(this string s)
    {
        decimal d;
        return decimal.TryParse(s, System.Globalization.NumberStyles.Any, System.Globalization.CultureInfo.CurrentCulture, out d);
    }

    /// <summary>
    /// Returns true only if string is wholy comprised of numerical digits
    /// </summary>
    public static bool IsNumbersOnly(this string s)
    {
        if (s == null || s == string.Empty)
            return false;

        foreach (char c in s)
        {
            if (c < '0' || c > '9') // Avoid using .IsDigit or .IsNumeric as they will return true for other characters
                return false;
        }

        return true;
    }
}

Answer 20

public static bool IsNumeric(this string input)
{
    int n;
    if (!string.IsNullOrEmpty(input)) //.Replace('.',null).Replace(',',null)
    {
        foreach (var i in input)
        {
            if (!int.TryParse(i.ToString(), out n))
            {
                return false;
            }

        }
        return true;
    }
    return false;
}

Answer 21

Hope this helps

string myString = "abc";
double num;
bool isNumber = double.TryParse(myString , out num);

if isNumber 
{
//string is number
}
else
{
//string is not a number
}

Answer 22

Pull in a reference to Visual Basic in your project and use its Information.IsNumeric method such as shown below and be able to capture floats as well as integers unlike the answer above which only catches ints.

    // Using Microsoft.VisualBasic;

    var txt = "ABCDEFG";

    if (Information.IsNumeric(txt))
        Console.WriteLine ("Numeric");

IsNumeric("12.3"); // true
IsNumeric("1"); // true
IsNumeric("abc"); // false

Answer 23

All the Answers are Useful. But while searching for a solution where the Numeric value is 12 digits or more (in my case), then while debugging, I found the following solution useful :

double tempInt = 0;
bool result = double.TryParse("Your_12_Digit_Or_more_StringValue", out tempInt);

Th result variable will give you true or false.

Answer 24

Regex rx = new Regex(@"^([1-9]\d*(\.)\d*|0?(\.)\d*[1-9]\d*|[1-9]\d*)$");
string text = "12.0";
var result = rx.IsMatch(text);
Console.WriteLine(result);

To check string is uint, ulong or contains only digits one .(dot) and digits Sample inputs

123 => True
123.1 => True
0.123 => True
.123 => True
0.2 => True
3452.434.43=> False
2342f43.34 => False
svasad.324 => False
3215.afa => False

Answer 25

Here is the C# method. Int.TryParse Method (String, Int32)

Answer 26

//To my knowledge I did this in a simple way
static void Main(string[] args)
{
    string a, b;
    int f1, f2, x, y;
    Console.WriteLine("Enter two inputs");
    a = Convert.ToString(Console.ReadLine());
    b = Console.ReadLine();
    f1 = find(a);
    f2 = find(b);

    if (f1 == 0 && f2 == 0)
    {
        x = Convert.ToInt32(a);
        y = Convert.ToInt32(b);
        Console.WriteLine("Two inputs r number \n so that addition of these text box is= " + (x + y).ToString());
    }
    else
        Console.WriteLine("One or two inputs r string \n so that concatenation of these text box is = " + (a + b));
    Console.ReadKey();
}

static int find(string s)
{
    string s1 = "";
    int f;
    for (int i = 0; i < s.Length; i++)
       for (int j = 0; j <= 9; j++)
       {
           string c = j.ToString();
           if (c[0] == s[i])
           {
               s1 += c[0];
           }
       }

    if (s == s1)
        f = 0;
    else
        f = 1;

    return f;
}