如何在沒有第三個變量的情況下交換兩個變量的值？

1、 int a= 3, b = 4;
a = a + b;
b = a - b;

a = a - b;

2、 int a = 3, b = 4;
a = a ^ b;
b = a ^ b;
a = a ^ b;

3、 int a = 3, b = 4;

a = b+(b=a)*0;