#include <stdio.h>

void addZerosAt(int * a, int N, int p1, int p2)
{
    if (p1 > p2)
    {
        int p = p1;
        p1 = p2;
        p2 = p;
    }
    for(int i = N+1; i >= p1; --i)
    {
        if (i > p2) a[i] = a[i-2];
        else a[i] = a[i-1];
    }
    a[p1] = a[p2] = 0;
}


int main(int argc, const char * argv[])
{
    int a[20] = { 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
    for(int i = 0; i < 15; ++i) printf("%2d ",a[i]); puts("");
    addZerosAt(a,15,5,12);
    for(int i = 0; i < 17; ++i) printf("%2d ",a[i]); puts("");
}