first write the given number in it's binary format.
am considering only 8 bit at a time , 
5- 0000 0101
step 1: convert this binary format to one's compliment (ie)
change 0 to 1 and 1 to 0.
1111 1010

step 2: add 1 to the above binary format.

1111 1010
        1
-----------
1111 1011

so this binary format will get stored in memory and the sign
bit will be set to 1.

always the negative number will be stored only in 2's
compliment..........


thank u