程序代码：

void swapr(int &a, int &b);
void swapp(int *p, int *q);
void swapv(int a, int b);

int main()
{
    int wallet1 = 300;
    int wallet2 = 350;
    
    cout << "wallet1 = $" << wallet1;
    cout << " wallet2 = $" << wallet2 << endl;
    
    cout << "using references to swap contents: " << endl;
    swapr(wallet1, wallet2);
    cout << "wallet1 = $" << wallet1;
    cout << " wallet2 = $" << wallet2 << endl;
    
    cout << "using pointers to swap contents again: " << endl;
    swapp(&wallet1, &wallet2);
    cout << "wallet1 = $" << wallet1;
    cout << " wallet2 = $" << wallet2 << endl;
    
    cout << "trying use passing by value:" << endl;
    swapv(wallet1, wallet2);
    cout << "wallet1 = $" << wallet1;
    cout <<" wallet2 = $" << wallet2 << endl;
    
    return 0;
}

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

void swapp(int *p, int *q)
{   
    int temp;
    
    temp = *p;
    *p = *q;
    *q = temp;
}

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