Why AND two numbers to get a Boolean?

Question

I am working on a little Hardware interface project based on the Velleman k8055 board.

The example code comes in VB.Net and I'm rewriting this into C#, mostly to have a chance to step through the code and make sense of it all.

One thing has me baffled though:

At one stage they read all digital inputs and then set a checkbox based on the answer to the read digital inputs (which come back in an Integer) and then they AND this with a number:

i = ReadAllDigital
cbi(1).Checked = (i And 1)
cbi(2).Checked = (i And 2) \ 2
cbi(3).Checked = (i And 4) \ 4
cbi(4).Checked = (i And 8) \ 8
cbi(5).Checked = (i And 16) \ 16

I have not done Digital systems in a while and I understand what they are trying to do but what effect would it have to AND two numbers? Doesn't everything above 0 equate to true?

How would you translate this to C#?

Answer 1

This is doing a bitwise AND, not a logical AND.

Each of those basically determines whether a single bit in i is set, for instance:

5 AND 4 = 4
5 AND 2 = 0
5 AND 1 = 1

(Because 5 = binary 101, and 4, 2 and 1 are the decimal values of binary 100, 010 and 001 respectively.)