Bit operations: Clear a bit
	Problem: given int i, set bit n to 0
							bn			b0
		i	0000	0000	0000	0000	0000	0000	0000	0010
							bit n
		How can we make sure this bit is 0 (and not affect any other bits)?
		We can use & operator with a "mask":
		mask	1111	1111	1111	1111	1101	1111	1111	1111
		i &= mask;
	What is the problem with this?
	Answer:
		i &= ~(1 << n);			/* idiom */
		Shift 1 bit n places to the left
		Flip bits to get all 1's except 0 in bit n
		Apply & operator to clear bit n