Advertisement
Advertisement


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?

2019/01/29
1
752
1/29/2019 6:23:17 PM

Accepted Answer

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!

2020/02/14
1192
2/14/2020 1:37:06 PM

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.

2009/05/21

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.

2018/04/30

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

alt text
(source: aspalliance.com)

alt text
(source: aspalliance.com)

2019/03/17

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.

2016/05/31

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

2014/02/27

Source: https://stackoverflow.com/questions/894263
Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Email: [email protected]