Programming in C

Bit Operators
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The second printf call results in the display of octal 77,which is the result of
ANDing word1 with itself. By definition, any quantity x,when ANDed with itself, produces
x.
The third printf call displays the result of ANDing word1, word2,and word3 together.The
operation of bitwise ANDing is such that it makes no difference whether an
expression such as a & b & c is evaluated as (a & b) & c or as a & (b & c),but for
the record, evaluation proceeds from left to right. It is left as an exercise to you to verify
that the displayed result of octal 10 is the correct result of ANDing word1 with word2
with word3.
The final printf call has the effect of extracting the rightmost bit of word1.This is
actually another way of testing if an integer is even or odd because that rightmost bit of
any odd integer is 1 and of any even integer is 0.Therefore when the if statement
if ( word1 & 1 )
...
is executed, the expression is true if word1 is odd (because the result of the AND operation
is 1) and false if it is even (because the result of the AND operation is 0). (Note: On
machines that use a ones complement representation for numbers, this does not work for
negative integers.)
The Bitwise Inclusive-OR Operator
When two values are bitwise Inclusive-ORed in C, the binary representation of the two
values are once again compared bit by bit.This time, each bit that is a 1 in the first value
or a 1 in the second value produces a 1 in the corresponding bit of the result.The truth
table for the Inclusive-OR operator is shown next.
b1 b2 b1 | b2
----------------------------------------
0 0 0
0 1 1
1 0 1
1 1 1
So, if w1 is an unsigned int equal to octal 0431 and w2 is an unsigned int equal to
octal 0152, then a bitwise Inclusive-OR of w1 and w2 produces a result of octal 0573 as
shown:
w1 ... 100 011 001 0431
w2 ... 001 101 010 | 0152
------------------------------
... 101 111 011 0573
As was pointed out with the bitwise AND operator, be sure to not confuse the operation
of bitwise ORing (|) with that of logical ORing (||), the latter operation being
used to determine if either of two logical values is true.