Char.IsDigit

This C# method checks character values. It determines if a character in the string is a digit character—meaning it is part of an Arabic number—in the range 0-9.

IsDigit is useful in parsing, scanning or sorting algorithms. It simply tests the range of the char value. And this logic can be extracted from IsDigit.

Input and output

Consider the string "abc123." The char.IsDigit method should return false 3 times, and then true 3 times, in a string loop.

a -> false
b -> false
c -> false
1 -> true
2 -> true
3 -> true

First example

IsDigit() is a static method on the System.Char struct, which is aliased to the char keyword. It returns true if the character is a digit character.

using System;

class Program
{
    static void Main()
    {
        string test = "Abc,123";
        foreach (char value in test)
        {
            bool digit = char.IsDigit(value);
            Console.Write(value);
            Console.Write(' ');
            Console.WriteLine(digit);
        }
    }

    /// <summary>
    /// Returns whether the char is a digit char.
    /// Taken from inside the char.IsDigit method.
    /// </summary>
    public static bool IsCharDigit(char c)
    {
        return ((c >= '0') && (c <= '9'));
    }
}
A False
b False
c False
, False
1 True
2 True
3 True

The C# char.IsDigit method tests for digits between 0 and 9. You can extract the character-testing logic for more predictable behavior and slightly better performance.