Comments on: How to check a given number is exact power of two?

By: udhaya

udhaya — Wed, 31 Mar 2010 11:47:20 +0000

Find if the given number is a power of 2.
//include math.h

void main()
{
int n,logval,powval;
printf(“Enter a number to find whether it is s power of 2\n”);
scanf(“%d”,&n);
logval=log(n)/log(2);
powval=pow(2,logval);
if(powval==n)
printf(“The number is a power of 2″);
else
printf(“The number is not a power of 2″);
getch();
}

By: Rick

Rick — Wed, 18 Feb 2009 14:33:38 +0000

Somehow my comment got cut off. It’s supposed to say “Since n is an int, it could be less than or equal to 0″. You need to add a check for this.

By: Rick

Rick — Wed, 18 Feb 2009 14:28:09 +0000

Zero is not a power of two, nor are negative numbers. Since n is an int, it could be 0) && (n&(n-1))==0);

See my article http://www.exploringbinary.com/ten-ways-to-check-if-an-integer-is-a-power-of-two-in-c/ . Specifically, the sections “9. Decrement and Compare” and “How NOT to Check”

Rick Regan

By: Faisal

Faisal — Fri, 24 Oct 2008 12:46:19 +0000

This code also work in the same way
return (value & -value) == value;