How to find a number in a string in C#?

To find a number in a string in C#, you can use Regular Expressions (Regex) from the System.Text.RegularExpressions namespace. The Regex pattern \d+ matches one or more consecutive digits in a string.

Syntax

Following is the syntax for creating a Regex pattern to match numbers −

Regex regex = new Regex(@"\d+");
Match match = regex.Match(inputString);

Following is the syntax for checking if a match was found −

if (match.Success) {
    string number = match.Value;
}

Using Regex to Find the First Number

The Match method finds the first occurrence of a number in the string −

using System;
using System.Text.RegularExpressions;

class Demo {
    static void Main() {
        Regex r = new Regex(@"\d+");
        Match m = r.Match("Welcome! We are open 365 days in a year!");

        if (m.Success) {
            Console.Write("Number: ");
            Console.WriteLine(m.Value);
        }
    }
}

The output of the above code is −

Number: 365

Using Regex to Find All Numbers

To find all numbers in a string, use the Matches method which returns a collection of all matches −

using System;
using System.Text.RegularExpressions;

class Demo {
    static void Main() {
        Regex r = new Regex(@"\d+");
        MatchCollection matches = r.Matches("We have 25 apples and 30 oranges, total 55 fruits.");

        Console.WriteLine("Found " + matches.Count + " numbers:");
        foreach (Match match in matches) {
            Console.WriteLine(match.Value);
        }
    }
}

The output of the above code is −

Found 3 numbers:
25
30
55

Using Different Regex Patterns

You can use different patterns to match specific types of numbers −

using System;
using System.Text.RegularExpressions;

class Demo {
    static void Main() {
        string text = "Price: $12.99, Discount: -5%, Temperature: 23.5°C";

        // Match integers only
        Regex integers = new Regex(@"\b\d+\b");
        Console.WriteLine("Integers: " + string.Join(", ", integers.Matches(text)));

        // Match decimal numbers
        Regex decimals = new Regex(@"\d+\.\d+");
        Console.WriteLine("Decimals: " + string.Join(", ", decimals.Matches(text)));

        // Match negative numbers
        Regex negatives = new Regex(@"-\d+");
        Console.WriteLine("Negative numbers: " + string.Join(", ", negatives.Matches(text)));
    }
}

The output of the above code is −

Integers: 12, 99, 5, 23, 5
Decimals: 12.99, 23.5
Negative numbers: -5

Comparison of Common Regex Patterns

Conclusion

Regular Expressions provide a powerful way to find numbers in strings using patterns like \d+ for basic digits. Use Match for the first occurrence, Matches for all occurrences, and customize patterns based on whether you need integers, decimals, or negative numbers.