Question

unsigned long long n = 0;
for (int i = 0; i <= 64; i+=2)
    n |= 1ULL << i;       //WHAT DOES THIS DO? AH! 

I’m trying to wrap my head around what the third line of this code actually does. Someone please help clear this up!

Answer 1

That line sets the i^th bit of n.

• 1ULL is the integer 1 with type unsigned long long.
• << is a bitshift operator. 1ULL << i is equal to 2ⁱ, or in binary: 100...0 with i zeros.
• n |= x; is a compound assignment operator. It is similar to writing n = n | x;.
• The operator | is the bitwise OR operator.

Wikipedia has an example showing how bitwise OR operator works in the general case:

   0101 (decimal 5)
OR 0011 (decimal 3)
 = 0111 (decimal 7)

Related

• What are bitwise shift (bit-shift) operators and how do they work?
• Bitwise operation