count the bits ON

Question

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

Alan · Answer

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 Montano · Answer

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.

Sam · Answer

Good Point. I didn't consider negative numbers.

Alan · Answer

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.

Sam · Answer

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 Montano · Answer

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; }

Alan · Answer

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 { if (bits[i] == '1') count++; } return count; } }

count the bits ON

Answers (7)