How to convert numbers between hexadecimal and decimal

To convert from decimal to hex do...

string hexValue = decValue.ToString("X");

To convert from hex to decimal do either...

int decValue = int.Parse(hexValue, System.Globalization.NumberStyles.HexNumber);

or

int decValue = Convert.ToInt32(hexValue, 16);

Hex -> decimal:

Convert.ToInt64(hexValue, 16);

Decimal -> Hex

string.format("{0:x}", decValue);

It looks like you can say

Convert.ToInt64(value, 16)

to get the decimal from hexdecimal.

The other way around is:

otherVar.ToString("X");

From Geekpedia:

// Store integer 182
int decValue = 182;

// Convert integer 182 as a hex in a string variable
string hexValue = decValue.ToString("X");

// Convert the hex string back to the number
int decAgain = int.Parse(hexValue, System.Globalization.NumberStyles.HexNumber);

String stringrep = myintvar.ToString("X");

int num = int.Parse("FF", System.Globalization.NumberStyles.HexNumber);

    static string chex(byte e)                  // Convert a byte to a string representing that byte in hexadecimal
    {
        string r = "";
        string chars = "0123456789ABCDEF";
        r += chars[e >> 4];
        return r += chars[e &= 0x0F];
    }           // Easy enough...

    static byte CRAZY_BYTE(string t, int i)     // Take a byte, if zero return zero, else throw exception (i=0 means false, i>0 means true)
    {
        if (i == 0) return 0;
        throw new Exception(t);
    }

    static byte hbyte(string e)                 // Take 2 characters: these are hex chars, convert it to a byte
    {                                           // WARNING: This code will make small children cry. Rated R.
        e = e.ToUpper(); // 
        string msg = "INVALID CHARS";           // The message that will be thrown if the hex str is invalid

        byte[] t = new byte[]                   // Gets the 2 characters and puts them in seperate entries in a byte array.
        {                                       // This will throw an exception if (e.Length != 2).
            (byte)e[CRAZY_BYTE("INVALID LENGTH", e.Length ^ 0x02)], 
            (byte)e[0x01] 
        };

        for (byte i = 0x00; i < 0x02; i++)      // Convert those [ascii] characters to [hexadecimal] characters. Error out if either character is invalid.
        {
            t[i] -= (byte)((t[i] >= 0x30) ? 0x30 : CRAZY_BYTE(msg, 0x01));                                  // Check for 0-9
            t[i] -= (byte)((!(t[i] < 0x0A)) ? (t[i] >= 0x11 ? 0x07 : CRAZY_BYTE(msg, 0x01)) : 0x00);        // Check for A-F
        }           

        return t[0x01] |= t[0x00] <<= 0x04;     // The moment of truth.
    }

This is not really easiest way but this source code enable you to right any types of octal number i.e 23.214, 23 and 0.512 and so on. Hope this will help you..

    public string octal_to_decimal(string m_value)
    {
        double i, j, x = 0;
        Int64 main_value;
        int k = 0;
        bool pw = true, ch;
        int position_pt = m_value.IndexOf(".");
        if (position_pt == -1)
        {
            main_value = Convert.ToInt64(m_value);
            ch = false;
        }
        else
        {
            main_value = Convert.ToInt64(m_value.Remove(position_pt, m_value.Length - position_pt));
            ch = true;
        }

        while (k <= 1)
        {
            do
            {
                i = main_value % 10;                                        // Return Remainder
                i = i * Convert.ToDouble(Math.Pow(8, x));                   // calculate power
                if (pw)
                    x++;
                else
                    x--;
                o_to_d = o_to_d + i;                                        // Saving Required calculated value in main variable
                main_value = main_value / 10;                               // Dividing the main value 
            }
            while (main_value >= 1);
            if (ch)
            {
                k++;
                main_value = Convert.ToInt64(Reversestring(m_value.Remove(0, position_pt + 1)));
            }
            else
                k = 2;
            pw = false;
            x = -1;
        }
        return (Convert.ToString(o_to_d));
    }    

This one worked for me:

public static decimal HexToDec(string hex)
{
  if (hex.Length % 2 == 1)
    hex = "0" + hex;
  byte[] raw = new byte[hex.Length / 2];
  decimal d = 0;
    for (int i = 0; i < raw.Length; i++)
    {
      raw[i] = Convert.ToByte(hex.Substring(i * 2, 2), 16);
      d += Math.Pow(256, (raw.Length - 1 - i)) * raw[i];
    }
    return d.ToString();
  return d;
}

Decimal - Hexa

        var decValue = int.Parse(Console.ReadLine());
        string hex = string.Format("{0:x}", decValue);
        Console.WriteLine(hex);

Hexa - Decimal (use namespace: using System.Globalization;)

        var hexval = Console.ReadLine();
        int decValue = int.Parse(hexval, NumberStyles.HexNumber);
        Console.WriteLine(decValue);

You can use this code and possible set Hex length and part's:

const int decimal_places = 4;
const int int_places = 4;
static readonly string decimal_places_format = $"X{decimal_places}";
static readonly string int_places_format = $"X{int_places}";

public static string DecimaltoHex(decimal number)
{
    var n = (int)Math.Truncate(number);
    var f = (int)Math.Truncate((number - n) * ((decimal)Math.Pow(10, decimal_places)));
    return $"{string.Format($"{{0:{int_places_format}}}", n)}{string.Format($"{{0:{decimal_places_format}}}", f)}";
}

public static decimal HextoDecimal(string number)
{
    var n = number.Substring(0, number.Length - decimal_places);
    var f = number.Substring(number.Length - decimal_places);
    return decimal.Parse($"{int.Parse(n, System.Globalization.NumberStyles.HexNumber)}.{int.Parse(f, System.Globalization.NumberStyles.HexNumber)}");
}

FOUR C# native ways to convert Hex to Dec and back:

using System;

namespace Hexadecimal_and_Decimal
{
  internal class Program
  {
    private static void Main(string[] args)
    {
      string hex = "4DEAD";
      int dec;

      // hex to dec:
      dec = int.Parse(hex, System.Globalization.NumberStyles.HexNumber);
      // or:
      dec = Convert.ToInt32(hex, 16);

      // dec to hex:
      hex = dec.ToString("X"); // lowcase: x, uppercase: X
      // or:
      hex = string.Format("{0:X}", dec); // lowcase: x, uppercase: X

      Console.WriteLine("Hexadecimal number: " + hex);
      Console.WriteLine("Decimal number: " + dec);
    }
  }
}

My solution is a bit like back to basics, but it works without using any built-in functions to convert between number systems.

    public static string DecToHex(long a)
    {
        int n = 1;
        long b = a;
        while (b > 15)
        {
            b /= 16;
            n++;
        }
        string[] t = new string[n];
        int i = 0, j = n - 1;
        do
        {
                 if (a % 16 == 10) t[i] = "A";
            else if (a % 16 == 11) t[i] = "B";
            else if (a % 16 == 12) t[i] = "C";
            else if (a % 16 == 13) t[i] = "D";
            else if (a % 16 == 14) t[i] = "E";
            else if (a % 16 == 15) t[i] = "F";
            else t[i] = (a % 16).ToString();
            a /= 16;
            i++;
        }
        while ((a * 16) > 15);
        string[] r = new string[n];
        for (i = 0; i < n; i++)
        {
            r[i] = t[j];
            j--;
        }
        string res = string.Concat(r);
        return res;
    }