#include <iostream>

using namespace std;

// prototype for pass-by-value
int negX(int i);

// prototype for reference
void negXbyRef(int &y);

// prototype for pointer
void negX(int *y);

// negation of x 
int main() {
  int x = 0;

  // I/O
  cout << endl << "Please enter an integer: ";
  cin >> x;

  // calculation w/o function
  cout << "Original x: " << x << endl;
  x = -x;
  cout << "New x: " << x << endl;

  /* * * PASS BY VALUE * * */
  cout << endl << "*** PASS BY VALUE ***" << endl;
  cout << "Before the function x = " << x << endl;
  x = negX(x);
  cout << "Negative x (or what is now x's value): " << x << endl;

  /* * * PASS BY REFERENCE * * */
  cout << endl << "*** PASS BY REFERENCE ***" << endl;
  cout << "Before pass by reference x = " << x << endl;
  negXbyRef(x);
  cout << "Negative x (or what is now x's value): " << x << endl;

  /* * * POINTERS (ADDRESSES) * * */
  cout << endl << "*** POINTERS ***" << endl;
  cout << "Original x = " << x << endl;
  negX(&x);
  cout << "Negative x (or what is now x's value): " << x << endl;

  return 0;
}

// pass-by-value
int negX(int k) {
  return -k;
}

// using references
void negXbyRef(int &z) {
  z *= -1;
}

// using pointers
void negX(int *z) {
  *z *= -1;
}