main()
{
 int a=5,b=3;
b=a+b;
a=b-a;
b=b-a;
printf(" %d   %d ",a,b);
}

main()
{
 int a=5,b=3;
a=a+b;
b=a-b;
a=a-b;
printf(" %d   %d ",a,b);
getch();
}

Questions is to swap the string  not for integers so the
above answers are wrong.

void main()
{
 char *p="string1";
 char *q="string2";

 p^=q^=p^=q;
 printf("%s,%s",p,q);
}

swapping the base pointers of the two strings may work... 
if they are declared as character arrays, then it is not 
possible as we cannot modify the value of array base 
pointers...

main()
{
 int a=5,b=3;
a=a+b;
b=a-b;
a=a-b;
printf(" %d   %d ",a,b);
getch();
}