How to Exchange two variables without any third variable?

Exchange two variable without third variable

This looks very tricky but not very hard to think a logic for this. Let say we have two variables A and B. Now we can add them and store in A. At this point A contains value of A plus B i.e. A = A + B. Now say subtract B from it (A - B). We can get value of A and store it in B i.e. B = A - B. Now B contains value of A. We are almost half done. Now subtract B from it which is actually contains value of A to get the value of B in A i.e. A = A - B. We are done exchange these two. Let construct a C program.

Source Code

 #include <stdio.h>

 int main (int argc, char *argv[])

 {

   int A = 1, B = 2;

   printf ("A = %d, B = %d\n");

   printf ("Exchanging A <> B\n");

   A = (A + B);

   B = A - B; /* equal to (A + B) - B == A */

   A = A - B; /* equal to (A + B) - B (Value of A) == B */

   printf ("A = %d, B = %d\n");

   return (0);

 }

Output

A = 2, B = 1
Exchanging A <> B
A = 1, B = 2

A = -2, B = -1
Exchanging A <> B
A = -1, B = -2

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