#include <cassert>   // assert
#include <iostream>  // std::cout

/*
 * pass an integer argument by value
 */
void pass_by_value(int n)
{
   std::cout << "pass_by_value(" << n << ").\n";
   n = 5;
}

/*
 * pass an integer argument by reference, using a pointer
 */
void pass_by_reference_a(int* pointer_to_n)
{
   std::cout << "pass_by_reference_a(" << pointer_to_n << ").\n";
   assert(pointer_to_n != nullptr);  // often a good idea to check
   
   *pointer_to_n = 5;
}

/*
 * pass an integer argument by reference, using a pointer
 * 
 * note: the int is passed by reference, but the int* is passed by value
 */
void pass_by_reference_b(int* pointer_to_n)
{
   std::cout << "pass_by_reference_b(" << pointer_to_n << ").\n";
   assert(pointer_to_n != nullptr);  // often a good idea to check
   
   pointer_to_n = nullptr;  // make the pointer point to the address 0
}

/*
 * pass an integer argument by reference, using a reference
 */
void pass_by_reference_c(int& n)
{
   std::cout << "pass_by_reference_c(" << n << ").\n";
   n = 5;
}

int main()
{
   int k{};
   int* pointer_to_k = &k;
   
   // pass k = 4 by value
   //
   k = 4;
   pass_by_value(k);
   std::cout << "\tk = " << k << ".\n\n";
   
   // pass k = 4 by reference, using a pointer value (memory address &k)
   // the code dereferences the pointer and writes 5 into its address
   //
   k = 4;
   pass_by_reference_a(pointer_to_k);
   std::cout << "\tk = " << k << ".\n\n";
   
   // pass k = 4 by reference, using a pointer value (memory address &k)
   // the code assigns a new memory address to the pointer
   // note that the pointer is being passed by value
   //
   k = 4;
   pass_by_reference_b(pointer_to_k);
   std::cout << "\tk = " << *pointer_to_k << ".\n\n";
   
   // pass k = 4 by reference, using a reference
   //
   // this is equivalent to using a pointer, except that it hides the
   // referencing and dereferencing from the programmer; accessing the
   // reference "looks like" accessing the variable
   //
   k = 4;
   pass_by_reference_c(k);
   std::cout << "\tk = " << k << ".\n\n";
}