From Any To Any Numeral System

using System;
using System.Linq;

public class ConvertFromAnyNumSystem
{
    static void Main()
    {
        // user input
        Console.Write("Enter a number: ");
        string number = (Console.ReadLine()).ToUpper();
        Console.Write("Enter numberal system to convert From: ");
        int s = int.Parse(Console.ReadLine());
        Console.Write("Enter numberal system to convert To: ");
        int d = int.Parse(Console.ReadLine());

        // validation - input numbers are to be in the required range: (2 ≤ s, d ≤ 16)
        if (s < 2 || d < 2 || d > 16 || s > 16)
        {
            Console.WriteLine("Wrong input!Number should be in range [2 to 16]");
        }
        else
        {
            // applying the ConvertToDec(number, s) method on the input numbers,
            // and applying the DecimalToBase() method on the result
            Console.WriteLine(DecimalToBase(ConvertToDec(number, s), d));
        }
    }

    // converting all input numbers to decimal numeral system first
    public static int ConvertToDec(string number, int baseFrom)
    {
        int decNum = 0;
        for (int i = 0; i < number.Length; i++)
        {
            if (number[i] > '9') // if a char digit is > '9', it can only be 'A', 'B', etc.
            //from the hexadecimal numeral system
            {
                decNum += (number[i] - '7') * (int)Math.Pow(baseFrom, (number.Length - 1 - i));
                // example: 'A' = 65 (ASCII code); '7' = 55; hence 'A' - '7' = 10,
                // which is exactly the decimal representation of the digit A
            }
            else
            {
                decNum += (number[i] - '0') * (int)Math.Pow(baseFrom, (number.Length - 1 - i));
                // example: '9' = 57 (ASCII code); '0' = 48; hence '9' - '0' = 9,
                // which is exactly the decimal value of the digit 9
            }
        }
        return decNum;
    }

    public static string DecimalToBase(long decimalNumber, int numeralSystem)
    {
        string result = "";
        while (decimalNumber > 0)
        {
            // calculating remainder, after the input number
            // is divided by the number representing the numeral system
            // and we obtain the input number's digits
            long digit = decimalNumber % numeralSystem;

            if (digit >= 0 && digit <= 9)
            // example: '9' = 57 (ASCII code); '0' = 48; hence 9 - '0' = 9 + 48 = 57,
            // which is exactly the ASCII code of the char '9'
            // and the result is actually a string of chars, representing the separate digits of the number
            {
                result += (char)(digit + '0'); // we add one more char to the string representation of the number
            }

            // if a digit is > 9, it can only be A, B, etc.
            //from the hexadecimal numeral system
            else
            {
                result += (char)(digit + '7');
                // example: 'A' = 65 (ASCII code); '7' = 55; hence A + '7' = 10 + 55 = 65,
                // which is exactly the ASCII code of the char 'A'
            }

            // we divvide the decimal number by the number representing the numeral system,
            // so that we can re-apply the code below, and keep extracting digits,
            // until the decimal number has no more digits
            // and all its digits have been converted to chars,
            // and added to the string representation of the result number
            decimalNumber /= numeralSystem;
        }
        var reversed = result.Reverse(); // we will extract the digits in reversed order, so we need to reverse the order back to the correct one
        string output = string.Join("", reversed);
        return output;
    }
}