## 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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