// filename: evensourceByFunctions.cpp
//
// Pointer Exercise #6
// Write a function countEven(int*, int) which receives an integer array
// and its size, and returns the number of even numbers in the array.
//
// An example of the use of pointers to traverse an array.
//
// In this program, three functions are shown, using the array index ([]) notation
// and the pointer (*) notation.  They are completely equivalent in the funcionality
// -- they are only syntactic variations.

#include <iostream>
using namespace std;

// prototypes
int countEven1(int a[], int size); // use the [] notation
int countEven2(int* a, int size);  // use the * notation and offset
int countEven3(int* a, int size);  // use the * notation and iterator

int main()
{
  int ar[5] = { 5, 2, 9, 4, 0 };
  int count;

  count = countEven1(ar, 5);
  cout << "countEven1 returned " << count << endl;

  count = countEven2(ar, 5);
  cout << "countEven2 returned " << count << endl;

  count = countEven3(ar, 5);
  cout << "countEven3 returned " << count << endl;

  return 0;
}

// This function uses the array index ([]) notation.
// Note the array parameter is "int a[]", NOT "int[] a" as in Java.
int countEven1(int a[], int size)
{
  int countLocal = 0;

  for (int i = 0; i < size; i++) {
    if (a[i] % 2 == 0) {
      countLocal++;
    }
  }

  return countLocal;
}

// This function uses the pointer (*) notation.
// The pointer a is in the parameter, and it points to the beginning
// of the array passed in from the calling function.
// Each element in the array is accessed by its offset from the
// beginning of the array.
int countEven2(int* a, int size)
{
  int countLocal = 0;

  for (int i = 0; i < size; i++) {
    if (*(a + i) % 2 == 0) {
      countLocal++;
    }
  }

  return countLocal;
}

// This function uses the pointer (*) notation.
// The pointer a is in the parameter, and it points to the beginning
// of the array passed in from the calling function.
// The pointer gets advanced (by ++) when the code iterates through the array.
int countEven3(int* a, int size)
{
  int countLocal = 0;

  for (int i = 0; i < size; i++) {
    if (*a % 2 == 0) {
      countLocal++;
    }
    a++; // advance the pointer a by 1 slot
  }

  return countLocal;
}