#include <stdio.h>

#define NUM_ELEMS	8

int nums[NUM_ELEMS] = {17, -3, 6, -11, 25, 31, 0, 15};


int sum (int *array, int n)
{ 
    int i;
    int sum = 0;

    for (i = 0; i < n; i++)
	if (i % 2 == 0)
	        sum += array[i];
	else
		sum -= array[i];

    return sum; 
} 

int main ()
{
//    int nums[NUM_ELEMS] = {17, -3, 6, -11, 25, 31, 0, 15};

    int result = sum (nums, NUM_ELEMS);

    printf ("result is %d\n", result);
}