let
     A=10
     B=20
after swaping A=20
              B=10
ok   
      A = A + B  (A = 20+10 = 30)
      B = A - B  (B = 20-10 = 10)---->B=10
      A = A - B  (A = 30-10 = 20)---->A=20
Thats all very simple

byee Friends
rajendra
rajendra prasad reddy
rajendra_penumalli@yahoo.com
9885162742
hyd

sorry rejendra but i think u r wrong
u hae initially takn a=10 and b=20
ut had taken opposite values moreovr when u have performed
the operation a=a+b
now the value of a has become 30 not the previous 1
i think this will be done with the use of temp variable

Before Swaping
A = 10
B = 20
After Swapping
A = 20
B = 10

Solution:
B = B - A =(20-10) = 10 ---> B = 10
A = A + B =(10+10) = 20 ---> A = 20 (since B = 10 now)

a^=b
b^=a
a^=b

rajendra is correct

but the example he took is wrong...

sorry your question is wrong