OK, here's a C version. Had to add a parameter, of course:
void add1(int arr[], int length, int val, int n)
{
int direction = n >= 0;
int counter = n == 0 ? length : abs(n);
int index;
for(int i = 0; (i < length) && (counter != 0) ; i++)
{
index = direction ? i : length - i;
if(arr[index] == val)
{
arr[index]++;
counter--;
}
}
}