C# / .NET - check if string contains only letters

In this article, we would like to show you how to check if string contains only letters in C#.

Quick solution:

string text1 = "ABC";
string text2 = "ABC123";

string regex = "^[a-zA-Z]+$";

bool result1 = Regex.IsMatch(text1, regex); // True
bool result2 = Regex.IsMatch(text2, regex); // False

or:

string text1 = "ABC";
string text2 = "ABC123";

bool result1 = text1.All(Char.IsLetter); // True
bool result2 = text2.All(Char.IsLetter); // False

1. Practical example using regex

In this example, we use a regular expression (regex) with IsMatch() to check if the strings contain only letters.

using System;
using System.Text.RegularExpressions;

public class Program
{
    public static void Main()
    {
        string text1 = "ABC";
        string text2 = "ABC123";

        string regex = "^[a-zA-Z]+$";

        bool result1 = Regex.IsMatch(text1, regex);
        bool result2 = Regex.IsMatch(text2, regex);

        Console.WriteLine(result1); // True
        Console.WriteLine(result2); // False
    }
}

Output:

True
False

2. Using All() with IsLetter() method

In this example, we use All() from System.Linq with IsLetter() method to check if all characters in strings are letters.

using System;
using System.Linq;

public class Program
{
    public static void Main()
    {
        string text1 = "ABC";
        string text2 = "ABC123";

        bool result1 = text1.All(Char.IsLetter);
        bool result2 = text2.All(Char.IsLetter);

        Console.WriteLine(result1); // True
        Console.WriteLine(result2); // False
    }
}

Output:

True
False

References

1. Regex.IsMatch Method (System.Text.RegularExpressions) | Microsoft Docs
2. Enumerable.All<TSource>() Method (System.Linq) | Microsoft Docs
3. Char.IsLetter Method (System) | Microsoft Docs