Working example of passing by value, reference and pointer in every combination.

passing_by_example.cpp

// g++ passing_by_example.cpp -o passing_by_example.x && ./passing_by_example.x
#include <iostream>
using namespace std;

int main(){
  int Bats = 1;
  int *pB = &Bats;
  int& rB = Bats;

  void PassByValue(int b);
  void Reference(int &b);
  void Pointers(int *b);

  cout << "\nAt startup, within main() \tBats \t = " << Bats << endl;
  cout << endl;

  PassByValue(Bats);
  cout << "After calling PassByValue(Bats) Bats \t = " << Bats << endl;
  PassByValue(rB);
  cout << "After calling PassByValue(rB) \tBats \t = " << Bats << endl;
  PassByValue(*pB);
  cout << "After calling PassByValue(*pB) \tBats \t = " << Bats << endl;
  cout << endl;

  Reference(Bats);
  cout << "After calling Reference(Bats) \tBats \t = " << Bats << endl;
  Reference(rB);
  cout << "After calling Reference(rB) \tBats \t = " << Bats << endl;
  Reference(*pB);
  cout << "After calling Reference(*pB) \tBats \t = " << Bats << endl;
  cout << endl;

  Pointers(&Bats);
  cout << "After calling Pointers(&Bats) \tBats \t = " << Bats << endl;
  Pointers(pB);
  cout << "After calling Pointers(pB) \tBats \t = " << Bats << endl;
  Pointers(&rB);
  cout << "After calling Pointers(&rB) \tBats \t = " << Bats << endl;
  cout << endl;
}

void PassByValue(int b){
  b += 10;
  cout << "Within PassByValue() \t\tb \t = " << b << endl;
}

void Reference(int &b){
  b += 100;
  cout << "Within Reference() \t\tb \t = " << b << endl;
}

void Pointers(int *b){
  *b += 1000;
  cout << "Within Pointers() \t\t*b \t = " << *b << endl;
}

// Output:
//   At startup, within main()       Bats     = 1
//
//   Within PassByValue()            b        = 11
//   After calling PassByValue(Bats) Bats     = 1
//   Within PassByValue()            b        = 11
//   After calling PassByValue(rB)   Bats     = 1
//   Within PassByValue()            b        = 11
//   After calling PassByValue(*rB)  Bats     = 1
//
//   Within Reference()              b        = 101
//   After calling Reference(Bats)   Bats     = 101
//   Within Reference()              b        = 201
//   After calling Reference(rB)     Bats     = 201
//   Within Reference()              b        = 301
//   After calling Reference(*pB)    Bats     = 301
//
//   Within Pointers()               *b       = 1301
//   After calling Pointers(&Bats)   Bats     = 1301
//   Within Pointers()               *b       = 2301
//   After calling Pointers(pB)      Bats     = 2301
//   Within Pointers()               *b       = 3301
//   After calling Pointers(&rB)     Bats     = 3301
//
//