C# Program to Convert Decimal to Binary

Converting a decimal number to binary involves repeatedly dividing the decimal number by 2 and collecting the remainders. In C#, this can be accomplished using manual division or built-in methods like Convert.ToString().

The manual approach uses the division by 2 method where we divide the decimal number by 2, store the remainder, and continue until the quotient becomes 0. The binary representation is formed by reading the remainders in reverse order.

Using Manual Division Method

This method involves dividing the decimal number by 2 repeatedly and collecting remainders −

Example

using System;

class DecimalToBinaryConverter {
   static void Main() {
      int decVal = 34;
      string binary = "";
      
      Console.WriteLine("Decimal: {0}", decVal);
      
      int originalValue = decVal;
      while (decVal >= 1) {
         binary = (decVal % 2) + binary;
         decVal = decVal / 2;
      }
      
      Console.WriteLine("Binary: {0}", binary);
      Console.WriteLine("Verification: {0} decimal = {1} binary", originalValue, binary);
   }
}

The output of the above code is −

Decimal: 34
Binary: 100010
Verification: 34 decimal = 100010 binary

Using Built-in Convert.ToString() Method

C# provides the Convert.ToString() method with a base parameter to directly convert decimal to binary −

Example

using System;

class Program {
   static void Main() {
      int[] decimalNumbers = {34, 15, 255, 1024};
      
      Console.WriteLine("Decimal to Binary Conversion:");
      Console.WriteLine("-----------------------------");
      
      foreach (int decVal in decimalNumbers) {
         string binary = Convert.ToString(decVal, 2);
         Console.WriteLine("Decimal {0,4} = Binary {1,10}", decVal, binary);
      }
   }
}

The output of the above code is −

Decimal to Binary Conversion:
-----------------------------
Decimal   34 = Binary     100010
Decimal   15 = Binary       1111
Decimal  255 = Binary   11111111
Decimal 1024 = Binary 10000000000

Comparison of Methods

Using Recursive Approach

Example

using System;

class RecursiveBinaryConverter {
   static string DecimalToBinary(int decVal) {
      if (decVal == 0) return "0";
      if (decVal == 1) return "1";
      return DecimalToBinary(decVal / 2) + (decVal % 2).ToString();
   }
   
   static void Main() {
      int[] numbers = {0, 1, 8, 34, 100};
      
      Console.WriteLine("Recursive Binary Conversion:");
      Console.WriteLine("----------------------------");
      
      foreach (int num in numbers) {
         string binary = DecimalToBinary(num);
         Console.WriteLine("{0,3} ? {1,8}", num, binary);
      }
   }
}

The output of the above code is −

Recursive Binary Conversion:
----------------------------
  0 ?        0
  1 ?        1
  8 ?     1000
 34 ?   100010
100 ?  1100100

Conclusion

Converting decimal to binary in C# can be accomplished through manual division by 2, using Convert.ToString(decVal, 2), or recursion. The built-in method is most efficient for production use, while manual methods help understand the underlying conversion process.