#include <stdio.h>

int func(int *a, int b) {
	printf("a: %p\n", a);
	*a = *a + b;
	return *a;
}

int main() {

	int value = 10;
	int result;

	printf("prima vale: %d\n", value);
	printf("indirizzo: %p\n", &value);
	result = func(&value, 10);
	printf("dopo vale: %d\n", value);
	printf("risultato: %d\n", result);

	printf("prima vale: %d\n", value);
	result = func(&value, 15);
	printf("dopo vale: %d\n", value);
	printf("risultato: %d\n", result);

	return(0);
}

/*
 * The second way to pass a parameter is "by reference".
 *
 * You pass a parameter by reference whenever you pass a pointer instead
 * of a value.
 *
 * The function can change the value of the parameter outside its own
 * scope.
 *
 * Using the dereference operator (*) the programmer can write data at the
 * memory address (pointer) of a variable from within the function. 
 * Since the address of the variable is the same both inside and outside 
 * the scope of the function, then the value is changed program-wide.
 */

/*
 * E.g:
 *
 * int func(int *apointer) // the function takes a pointer argument!
 * {
 *   *apointer = ...; // changing the value at the specified address!
 *
 *   // the change is visible within the whole memory space of the program!
 *   ...
 * }
 *
 * int myvalue = ...;
 * ...
 *
 * func(&myvalue); // passing the addres!
 *                 // now the value of "myvalue" has changed!
 *...
 *
 */

/*
 * There are 3 reasons to pass an argument by reference:
 *
 * 1) You want a function to update the value of a variable,
 *
 *    e.g. add_income(&total, amount);
 *
 *    (add an amount to the total incomes).
 *
 * 2) You need your function to "return" more than one value,
 *
 *    e.g.: solve_triangle(A, B, C, &surface, &perimeter);
 *
 *    (given the lengths of the triangle sides A, B, and C calculate
 *    its surface and perimeter).
 *
 * 3) You are forced to! (e.g.: when passing arrays, see "array.c").
 */

/*
 * This function has 2 arguments: the first is passed by reference (it's
 * a pointer), the second is passed by value.
 *
 * The value at the memory address identified by the first parameter is
 * incremented by the value of the second.
 *
 * The value of the sum is returned.
 */