定义a=4,b=5，写3个重载函数swap，分别采用值传递、地址传递，引用传递3种方式，实现a,b值交换，请写出C++代码。

在C++中，我们可以分别为值传递、地址传递（即指针传递），以及引用传递编写三个`swap`函数来交换两个变量的值。这里是一个示例：

1. **值传递** (通过临时副本交换)：

void swapByValue(int a, int b) {
    int temp = a;
    a = b;
    b = temp;
}

int main() {
    int a = 4, b = 5;
    cout << "Before swap: a = " << a << ", b = " << b << endl;
    swapByValue(a, b);
    cout << "After swapByValue: a = " << a << ", b = " << b << endl;
    return 0;
}

2. **地址传递** (通过指针):

void swapByPointer(int* a, int* b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

int main() {
    int a = 4, b = 5;
    cout << "Before swap: a = " << a << ", b = " << b << endl;
    swapByPointer(&a, &b);
    cout << "After swapByPointer: a = " << a << ", b = " << b << endl;
    return 0;
}

3. **引用传递** (直接操作原址):

void swapByReference(int& a, int& b) {
    int temp = a;
    a = b;
    b = temp;
}

int main() {
    int a = 4, b = 5;
    cout << "Before swap: a = " << a << ", b = " << b << endl;
    swapByReference(a, b);
    cout << "After swapByReference: a = " << a << ", b = " << b << endl;
    return 0;
}