How to convert an integer to hexadecimal and vice versa in C#?

Converting integers to hexadecimal and vice versa is a common requirement in C# programming. C# provides several built-in methods to perform these conversions efficiently using ToString() for integer-to-hex conversion and Convert.ToInt32() or int.Parse() for hex-to-integer conversion.

Converting Integer to Hexadecimal

An integer can be converted to hexadecimal using the ToString() method with format specifiers −

Syntax

string hexValue = integerValue.ToString("X");   // Uppercase
string hexValue = integerValue.ToString("x");   // Lowercase
string hexValue = integerValue.ToString("X8");  // 8-digit padding

Example

using System;

public class Program {
   public static void Main() {
      int integerValue = 500;
      Console.WriteLine($"Integer Value: {integerValue}");
      
      string hexUppercase = integerValue.ToString("X");
      string hexLowercase = integerValue.ToString("x");
      string hexPadded = integerValue.ToString("X8");
      
      Console.WriteLine($"Hexadecimal (Uppercase): {hexUppercase}");
      Console.WriteLine($"Hexadecimal (Lowercase): {hexLowercase}");
      Console.WriteLine($"Hexadecimal (8-digit): {hexPadded}");
   }
}

The output of the above code is −

Integer Value: 500
Hexadecimal (Uppercase): 1F4
Hexadecimal (Lowercase): 1f4
Hexadecimal (8-digit): 000001F4

Converting Hexadecimal to Integer

A hexadecimal string can be converted to an integer using Convert.ToInt32() with base 16 or int.Parse() with NumberStyles.HexNumber −

Syntax

int value = Convert.ToInt32(hexString, 16);
int value = int.Parse(hexString, System.Globalization.NumberStyles.HexNumber);

Using Convert.ToInt32()

using System;

public class Program {
   public static void Main() {
      string hexValue = "1F4";
      Console.WriteLine($"Hexadecimal Value: {hexValue}");
      
      int integerValue = Convert.ToInt32(hexValue, 16);
      Console.WriteLine($"Integer Value: {integerValue}");
      
      // Works with lowercase too
      string hexLower = "ff";
      int intLower = Convert.ToInt32(hexLower, 16);
      Console.WriteLine($"Hex '{hexLower}' converts to: {intLower}");
   }
}

The output of the above code is −

Hexadecimal Value: 1F4
Integer Value: 500
Hex 'ff' converts to: 255

Using int.Parse() with NumberStyles

using System;
using System.Globalization;

public class Program {
   public static void Main() {
      string hexValue = "ABCD";
      Console.WriteLine($"Hexadecimal Value: {hexValue}");
      
      int integerValue = int.Parse(hexValue, NumberStyles.HexNumber);
      Console.WriteLine($"Integer Value: {integerValue}");
      
      // Convert back to verify
      string backToHex = integerValue.ToString("X");
      Console.WriteLine($"Back to Hex: {backToHex}");
   }
}

The output of the above code is −

Hexadecimal Value: ABCD
Integer Value: 43981
Back to Hex: ABCD

Comparison of Methods

Complete Conversion Example

using System;

public class HexConverter {
   public static void Main() {
      // Multiple integer values
      int[] numbers = {10, 255, 4096, 65535};
      
      Console.WriteLine("Integer to Hexadecimal Conversion:");
      foreach (int num in numbers) {
         string hex = num.ToString("X");
         Console.WriteLine($"{num} -> 0x{hex}");
      }
      
      Console.WriteLine("\nHexadecimal to Integer Conversion:");
      string[] hexValues = {"A", "FF", "1000", "FFFF"};
      
      foreach (string hex in hexValues) {
         int num = Convert.ToInt32(hex, 16);
         Console.WriteLine($"0x{hex} -> {num}");
      }
   }
}

The output of the above code is −

Integer to Hexadecimal Conversion:
10 -> 0xA
255 -> 0xFF
4096 -> 0x1000
65535 -> 0xFFFF

Hexadecimal to Integer Conversion:
0xA -> 10
0xFF -> 255
0x1000 -> 4096
0xFFFF -> 65535

Conclusion

Converting between integers and hexadecimal in C# is straightforward using ToString("X") for integer-to-hex and Convert.ToInt32(hex, 16) for hex-to-integer conversions. These methods handle both uppercase and lowercase hexadecimal formats and provide flexible formatting options for different use cases.