int array[] = { 2, 3, 4, 7, 10 };
int n = 18;

// Get smallest number
int smallest_number = 999;
for (int i = 0; i < length(array); i++)
    if (array[i] < smallest_number)
        smallest_number = array[i];

// If biggest number is at the end of your array - do it backwards:
// Do it as long (n > 0)
for (int i = length(array) - 1; i >= 0 && n > 0; i--) {
    // Can subtract from n
    if (array[index] > n)
        continue;

    // Array value is smaller or equal 'n'
    int new_value = n - array[index];
    if (new_value > 0 && new_value < smallest_number)
        continue;
    else
        n = new_value;

}