Subtraction

Objectives

We would like to :

Review the subtraction algorithm
Discuss subtraction in binary.

Notes

Can you subtract 372-134

  372   
- 134   
-----

2-4 we need to borrow a 1 from the 7
This becomes 12-4 = 8


   61
  372 
- 134   
-----
    8

  6-3 = 3

   61
  372  
- 134   
-----
   38

  3-1 = 2 

   61
  372   
- 134   
-----
  238

But it gets more complex, do 2000 - 1
We will not look at 22 - 123, yet because we don't have negative numbers.
We do use the addition table but in reverse
- Perform the barrow if necessary
- Find the first number inside the table.
- Find the second number on top/left
- Find the results on the left/top

So how do we subtract in binary?

The same way.

   101101  
-   10111
----------

1-1 = 0


   101101   
-   10111
----------
        0

0-1 = 1, with a borrow

      01
   101101  
-   10111
----------
       10

0-1 => 10-1 =  1, with a borrow


      1
     001
   101101   
-   10111
----------
      110

0 - 0= 0

      1
     001
   101101   
-   10111
----------
     0110

0-1 => 10-1 =  1, with a borrow

      1
    1001
   101101   
-   10111
----------
    10110