How can you swap two variables without a third variable in C?

main()
{
int a=5,b=7;
a=a+b;
b=a-b;
a=a-b;
printf("a=%d, b=%d", a, b);
}

or

main()
{
int a=5, b=7;
a = a ^ b;
b = a ^ b;
a = a ^ b;
printf("a=%d, b=%d", a, b);
}