Bit operations: Set a bit
Problem: given int i, set bit n to 1
    bn b0
i 0000 0000 0000 0000
0000
0000 0000 0010
bit n
How can we make sure this bit is set to1 (and not affect any other bits)?
We can use | operator with a "mask":
mask 0000 0000 0000 0000
0010
0000 0000 0000
i |= mask;
What is the problem with this?