Swapping two variables in place

[Theodore A. Camus]

>There was a message a while back about not being able to create a good
>#define function to swap two variables.
>
>How about this one: #define swap(a,b) a^=b^=a^=b

>But it won't work on `float's and `double's, as `^' is defined only on
>integral types.


Nor would it work for swap(i,A[i]).  
In fact, the usual { tmp = i ;  i = A[i] ; A[i] = tmp }  
would fail too.  Thus the danger of call-by-name.  

[ref 2nd Dragon book]



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