```#include <iostream>
using namespace std;

// Swap two variables using pass-by-value
void swap1(int n1, int n2)
{
int temp = n1;
n1 = n2;
n2 = temp;
}

// Swap two variables using pass-by-reference
void swap2(int& n1, int& n2)
{
int temp = n1;
n1 = n2;
n2 = temp;
}

// Pass two pointers by value
void swap3(int* p1, int* p2)
{
int temp = *p1;
*p1 = *p2;
*p2 = temp;
}

// Pass two pointers by reference
void swap4(int* &p1, int* &p2)
{
int* temp = p1;
p1 = p2;
p2 = temp;
}

int main()
{
// Declare and initialize variables
int num1 = 1;
int num2 = 2;

cout << "Before invoking the swap function, num1 is "
<< num1 << " and num2 is " << num2 << endl;

// Invoke the swap function to attempt to swap two variables
swap1(num1, num2);

cout << "After invoking the swap function, num1 is " << num1 <<
" and num2 is " << num2 << endl;

cout << "Before invoking the swap function, num1 is "
<< num1 << " and num2 is " << num2 << endl;

// Invoke the swap function to attempt to swap two variables
swap2(num1, num2);

cout << "After invoking the swap function, num1 is " << num1 <<
" and num2 is " << num2 << endl;

cout << "Before invoking the swap function, num1 is "
<< num1 << " and num2 is " << num2 << endl;

// Invoke the swap function to attempt to swap two variables
swap3(&num1, &num2);

cout << "After invoking the swap function, num1 is " << num1 <<
" and num2 is " << num2 << endl;

int* p1 = &num1;
int* p2 = &num2;
cout << "Before invoking the swap function, p1 is "
<< p1 << " and p2 is " << p2 << endl;

// Invoke the swap function to attempt to swap two variables
swap4(p1, p2);

cout << "After invoking the swap function, p1 is " << p1 <<
" and p2 is " << p2 << endl;

return 0;
}
```