Computing in Security (Conversion Help)
posted by Francesca on .
1.) Express each decimal number as an 8bit binary number in the 2's complement form and then find the negative of the representation of that number in two’s compliment
a.) +18
b) 117
Thanks for any help!

Two's complement is a notation that represents both positive and negative numbers. The most significant (leftmost) is the sign bit, which is turned on when the number is negative.
Unlike the one's complement, there is only one representation of zero.
For an eightbit number, the range goes from 128 to 127.
A positive number is represented by a usual binary number format, using the 7 loworder (rightmost) bits, and represent from 0 to 127.
A negative number is simply the reversal of the bits and then add 1.
Example:
10(decimal)=00001010(binary)
10(decimal)=11110101 + 1
=11110110
18(decimal)=00010010(binary)
18(decimal)=11101101 + 1
=11101110
and so on.
To negate a negative number, subtract one and reverse the bits.
For example,
18(decimal)=11101110
subtract 1
11101101
Reverse bits
00010010 (binary 18)