C/C++ 交换两个数，不使用第三个变量， 函数模板来实现

#include <iostream>

template<typename T>
void exchangeTwoNumber(T &t1, T &t2)；

void test();

int main()
{
    int a = , b = ;
    double q = 10.1, w = 20.2;
    char z = 'z', x = 'x';

    std::cout << "交换前的 a = " << a << ", b = " << b << std::endl;
    std::cout << "交换前的 q = " << q << ", w = " << w << std::endl;
    std::cout << "交换前的 z = " << z << ", x = " << x << std::endl;

    exchangeTwoNumber(a, b);
    exchangeTwoNumber(q, w);
    exchangeTwoNumber(z, x);
    test();

    std::cout << std::endl;
    std::cout << std::endl;
    std::cout << "交换后的    a = " << a << ",    b = " << b << std::endl;
    std::cout << "交换后的    q = " << q << ",    w = " << w << std::endl;
    std::cout << "交换后的    z = " << z << ",    z = " << x << std::endl;
}

template<typename T>
void exchangeTwoNumber(T &t1, T &t2)   //通用的函数模板
{
    t1 = t1 + t2;
    t2 = t1 - t2;
    t1 = t1 - t2;
}

void test()  //异或的方式，变形成函数模板，编译不通过
{
    int a = , b = ;
    a ^= b;
    b ^= a;
    a ^= b;

    std::cout << "...a=" << a << ", b=" << b << std::endl;
}