count the bits ON

ning ho

any idea how to design a function which returns the number of ON bits of an integer. ex, pass a number 1234 [Binary: 10011010010] returns 5, thanks

7 Replies

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Alan19y ago
Yeah, Convert.ToString(integer, 2) and Convert.ToString(integer, 8) compensate to some extent for C#'s lack of support for binary and octal literals. The omission of the latter was surprising as they're in C, C++ and Java but never mind - I never liked the syntax much anyway ;)
Jan Montano19y ago
Ooops. My bad. I didn't notice Convert.ToString(num, 2); in Alan's post above. It's a buit-in function alright. (^_^) Alan and Sam's solution is the way to go :) Don't mind my post above. hehehe.
Sam19y ago
Good Point. I didn't consider negative numbers.
Alan19y ago
Your probably right, Sam, that a method using integer arithmetic should be faster than one that uses a string function. However, the reason I used the latter is because it automatically deals with negative as well as positive integers which would require a bit more code in your version.
Sam19y ago
This is an alternative to Alan's function.
Since is uses maths instead of a convertion to string
it should be quicker (not 100% certain)

public static int ONBits(int x)
{
int count = 0;
while(x > 0)
{
    if ((x % 2) == 1)
    {
      count++;
    }
    x >>= 1;
}
   return count;
}
Jan Montano19y ago
For converting decimal values to binary values:
href=http://en.wikipedia.org/wiki/Binary_numeral_system#Decimal

I don't know if .Net has a buit-in function for converting decimal to binary values. listed below is one way of converting it.

static string ConvertToBinary(int decimalValue)
{

int remainder;
int quotient;

string binaryValue;

quotient = decimalValue / 2;
remainder = decimalValue % 2;

binaryValue = remainder.ToString();

while (quotient > 0)
{

remainder = quotient % 2;
quotient = quotient / 2;

binaryValue = remainder + binaryValue;

}

//Console.WriteLine("Binary Value of {0} is {1}", decimalValue, binaryValue);
return binaryValue;

}
Alan19y ago
Try this:

using System;

class Program
{
     static void Main()
     {
        int num = 1234;
        int count = GetBitsOnCount(num);
        Console.WriteLine("Number of bits on in {0} is {1}", num, count);
        Console.ReadLine();
     }

     public static int GetBitsOnCount(int num)
     {
        string bits = Convert.ToString(num, 2);
        int count = 0;
        for(int i = 0; i < bits.Length; i++)
        {
            if (bits[i] == '1') count++;
        }
        return count;
     }
}