Check if a string is a number in C#

This article illustrates the different techniques to check if a string is a number in C#.

1. Using `TryParse()` method

You can use the TryParse() method to identify if a string is a number. It works by converting the specified string to equivalent signed integer representation and returns true if the conversion succeeded; otherwise, false. Here’s what the code would look like:

using System;

public class Example

{

public static void Main()

{

string s = "123";

int n;

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

Console.WriteLine(n); // 123

Console.WriteLine(isNumeric); // True

}

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Note that the TryParse() method takes an Out parameter, which stores the integer value if the conversion was a success. This can be shortened to below if the Out parameter is not needed.

using System;

public class Example

{

public static void Main()

{

string s = "123";

bool isNumeric = int.TryParse(s, out _);

Console.WriteLine(isNumeric); // True

}

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Note that the Out parameter is declared and initialized in separate statements. Starting with C# 7, we can in-line declare and initialize the Out parameter.

using System;

public class Example

{

public static void Main()

{

string s = "123";

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

Console.WriteLine(n); // 123

Console.WriteLine(isNumeric); // True

}

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2. Using `Char.IsDigit()` method

The Char.IsDigit() method returns a boolean value indicating if the specified character is a digit. The following code example demonstrates the usage of the Char.IsDigit() method with the Enumerable.All() method to determine if a string is a number.

using System;

using System.Linq;

public class Example

{

public static void Main()

{

string s = "123";

bool isNumeric = s.All(char.IsDigit);

Console.WriteLine(isNumeric); // True

}

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3. Using `Regex.IsMatch()` method

Finally, you can use the regular expression to check if a string is numeric. This can be done using the Regex.IsMatch() method, which determines if the specified string matches with the supplied regex. This is demonstrated below. Note that ^ matches with the beginning of the string and $ match with its end.

using System;

using System.Text.RegularExpressions;

public class Example

{

public static void Main()

{

string s = "123";

bool isNumeric = Regex.IsMatch(s, @"^\d+$");

Console.WriteLine(isNumeric); // True

}

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That’s all about checking if a string is a number in C#.

Check if a string is a number in C#

1. Using TryParse() method

2. Using Char.IsDigit() method

3. Using Regex.IsMatch() method

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1. Using `TryParse()` method

2. Using `Char.IsDigit()` method

3. Using `Regex.IsMatch()` method