How to swap two variables, without using third variable ?

Swap two variables with out using third variable:

a=5,b=10
a=a+b;
b=a-b;
a=a-b;
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use xor to swap
a = a^b
b= a^b
a= a^b

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or
a=a*b;
b=a/b;
a=a/b;