Checking if a string ends with a number in C# is a very common operation. In this article, we are going to show various ways in which we can do this.Â
Let’s start.
Check if a String Ends With a Number Using IsDigit
Perhaps the most straightforward way of checking if a string ends with a number is by using the char.IsDigit method. We can use this method by passing in the last character of our string. This method is also pretty fast:
string inputString = "Hello1"; bool result = char.IsDigit(inputString.Last());
We can also modify this example to make it a bit faster:
bool result = char.IsDigit(inputString[^1]);
Check Using Character Comparison
A similar, yet slightly more complex method, is to again get the last character of the string and do a comparison with the 0 and 9 chars. Note that we use the digits as chars here, and not as integers, hence the apostrophes:
string inputString = "Hello1"; var lastChar = inputString.Last(); bool result = lastChar >= '0' && lastChar <= '9';
This is indeed slightly more complex, due to the comparison of characters, and also more prone to errors compared to the previous one-liner. However, it does allow one to finetune it further, e.g. by checking whether the last digit is equal to only 1, 2, or 3, but not the other digits.
Check Using Substring
The third way to check the same thing is by using the string.Substring method to get the last character of a string. The Substring method returns another string, to which we apply the IEnumerable.All method to check whether all elements (chars, in this case) satisfy a certain condition (char.IsDigit here):
string inputString = "Hello1"; bool result = inputString.Substring(inputString.Length - 1).All(char.IsDigit);
Even though this is slightly slower compared to the first solution, it is more flexible in that it allows us to easily get the last n characters, simply by changing the 1 into n. This way we can do the same check for the last n characters. In case we take multiple characters, we might even change the All method into Any. This allows us to check whether there is at least one digit character in the last n characters.Â
Using Regex to Check if a String Ends With a Number
Another way of doing this check is by using a regular expression:
string inputString = "Hello1"; var regex = new Regex(@"\d+$"); bool result = regex.Match(inputString).Success;
What we do is quite straightforward though: We create a new Regex checking whether the last character is a digit: $ matches the end of a string, while \d matches a digit. Regular expressions are extremely powerful and not only allow us to check whether a string ends with a digit, but we can easily modify it to extract that digit too. Take a look at our article about regular expressions in C# if you need to learn more or refresh your memory about it.
This method is also extremely fast, similar to doing the same using the last character and applying the IsDigit method on it.
Conclusion
In this article, we explored different methods of checking whether a string ends with a number in C#. We saw that even though all of them produce the same result, different methods might be preferred if we want to do slightly different operations.Â
Any benchmarks on those solutions ?
I would have definitely done this :
(instead of using Linq).
Hello Emy. We didn’t do benchmarks especially because there are so many variations for these examples. But, you are more than welcome to download our source code, add your example and create a simple benchmark, and of course, share the results. We will update the article gladly if we get better solutions
Here is my Benchmark class (With BenchmarkDotNet) and .NET 6 :
using BenchmarkDotNet.Attributes; using BenchmarkDotNet.Exporters; using BenchmarkDotNet.Mathematics; using BenchmarkDotNet.Order; using System.Linq; using System.Text.RegularExpressions; namespace SandboxBenchmark; [MemoryDiagnoser(false), MinColumn, MaxColumn] [RankColumn(NumeralSystem.Arabic)] [Orderer(SummaryOrderPolicy.FastestToSlowest)] [MarkdownExporter] public class LastDigitBenchmark { private const string shortWordInverted = "1Hello"; private const string shortWordWithoutAnyDigit = "Hello"; private const string shortWord = "Hello1"; private const string longSentence = "There's a growing trend among teenagers of using frisbees as go-cart wheels.\r\nHe went on a whiskey diet and immediately lost three days.\r\nShe saw no irony asking me to change but wanting me to accept her for who she is.\r\nhis seven-layer cake only had six layers.\r\nThe tortoise jumped into the lake with dreams of becoming a sea turtle.8"; private const string longSentenceInverted = "8There's a growing trend among teenagers of using frisbees as go-cart wheels.\r\nHe went on a whiskey diet and immediately lost three days.\r\nShe saw no irony asking me to change but wanting me to accept her for who she is.\r\nhis seven-layer cake only had six layers.\r\nThe tortoise jumped into the lake with dreams of becoming a sea turtle."; private const string longSentenceWithoutAnyDigit = "There's a growing trend among teenagers of using frisbees as go-cart wheels.\r\nHe went on a whiskey diet and immediately lost three days.\r\nShe saw no irony asking me to change but wanting me to accept her for who she is.\r\nhis seven-layer cake only had six layers.\r\nThe tortoise jumped into the lake with dreams of becoming a sea turtle."; [Benchmark] [Arguments(shortWordInverted)] [Arguments(shortWordWithoutAnyDigit)] [Arguments(shortWord)] [Arguments(longSentence)] [Arguments(longSentenceInverted)] [Arguments(longSentenceWithoutAnyDigit)] public bool CharIsDigitLinq(string inputString) => char.IsDigit(inputString.Last()); [Benchmark] [Arguments(shortWordInverted)] [Arguments(shortWordWithoutAnyDigit)] [Arguments(shortWord)] [Arguments(longSentence)] [Arguments(longSentenceInverted)] [Arguments(longSentenceWithoutAnyDigit)] public bool EqualityOperators(string inputString) { char lastChar = inputString.Last(); return lastChar >= '0' && lastChar <= '9'; } [Benchmark] [Arguments(shortWordInverted)] [Arguments(shortWordWithoutAnyDigit)] [Arguments(shortWord)] [Arguments(longSentence)] [Arguments(longSentenceInverted)] [Arguments(longSentenceWithoutAnyDigit)] public bool SubString(string inputString) => inputString.Substring(inputString.Length - 1).All(char.IsDigit); [Benchmark] [Arguments(shortWordInverted)] [Arguments(shortWordWithoutAnyDigit)] [Arguments(shortWord)] [Arguments(longSentence)] [Arguments(longSentenceInverted)] [Arguments(longSentenceWithoutAnyDigit)] public bool Regex(string inputString) { Regex regex = new(@"\d+$"); return regex.Match(inputString).Success; } [Benchmark] [Arguments(shortWordInverted)] [Arguments(shortWordWithoutAnyDigit)] [Arguments(shortWord)] [Arguments(longSentence)] [Arguments(longSentenceInverted)] [Arguments(longSentenceWithoutAnyDigit)] public bool CharIsDigitRangeOperator(string inputString) => char.IsDigit(inputString[^1]); }I have put in order of the article, each test, and added my proposition to the benchmark list at the end.
I also added 2 samples to test for each solution, one short (the article’s word) and one long sentence, as well as the invert of it.
Results have been attached as an image.
We can that the solution with the range operator ([^1]) is by far the better one. A few nano seconds or allocations of difference, but it may matter to someone.
Awesome. Thank you for sharing this. We will definitely update the article somehow to point out this solution as well.