Bug: negative numbers do not work

The the difference is always positive when subtracting.

Steps to reproduce:

% ./AddNums
Lets do some Math on two numbers
What type of operation would you like to perform
Add, Sub
Sub
Enter First Number:
-12
Enter Two Number:
4
Holly Shizzz the two Numbers EQUAL 08

% ./AddNums
Lets do some Math on two numbers
What type of operation would you like to perform
Add, Sub
Sub
Enter First Number:
10
Enter Two Number:
11
Holly Shizzz the two Numbers EQUAL 01

Also Add seems to completely ignore negative operands:

% ./AddNums
Lets do some Math on two numbers
What type of operation would you like to perform
Add, Sub
Add
Enter First Number:
-1
Enter Two Number:
2
Holly Shizzz the two Numbers EQUAL 03

I think this forum post helps us solve this critical bug:

http://www.ibmmainframeforum.com/ibm-cobol/topic11039.html