String - IsDigit

Indicates whether the character at the specified position in a specified string is categorized as a decimal digit.

Try it

public static void Main()
{
    string input = ".NET 4.7.2";

    Console.WriteLine("Is each of the following characters a digit?");

    for (int i = 0; i < input.Length; i++)
    {
		// C# Extension Method: String - IsDigit
		var result = input.IsDigit(i);
		
        Console.WriteLine("{0} : {1} ", input[i], result);
    }
}

View Source 
using System;

public static partial class Extensions
{
    /// <summary>
    ///     Indicates whether the character at the specified position in a specified string is categorized as a decimal
    ///     digit.
    /// </summary>
    /// <param name="s">A string.</param>
    /// <param name="index">The position of the character to evaluate in .</param>
    /// <returns>true if the character at position  in  is a decimal digit; otherwise, false.</returns>
    public static Boolean IsDigit(this String s, Int32 index)
    {
        return Char.IsDigit(s, index);
    }
}