How to convert numbers between hexadecimal and decimal

Question

How do you convert between hexadecimal numbers and decimal numbers in C#?

Answer 1

If it's a really big hex string beyond the capacity of the normal integer:

For .NET 3.5, we can use BouncyCastle's BigInteger class:

String hex = "68c7b05d0000000002f8";
// results in "494809724602834812404472"
String decimal = new Org.BouncyCastle.Math.BigInteger(hex, 16).ToString();

.NET 4.0 has the BigInteger class.

Answer 2

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;
    }

Answer 3

    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.
    }

Answer 4

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);

Answer 5

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);

Answer 6

It looks like you can say

Convert.ToInt64(value, 16)

to get the decimal from hexdecimal.

The other way around is:

otherVar.ToString("X");