Initialize a 40 digits array with 10 unique groups of 4 random digits

   srand(time(NULL));

            for (i = 4 - 1; i >= 0; i--)
            {
                // range is 0 - 9
                // buf[i] temporary int array to hold the groups of 4

                buf[i] = rand() % 10; 
                printf("digits: %d\n", buf[i]);

            }


            // Then I need to copy it to an int *numbers which is part of a 
            // struct
            for (i = 4 - 1; i >=0; i--)
            {
                n->numbers[i] = buf[i];
                //n->numbers[i+4] = buf[i];
                printf("arr1: %d\n", n->numbers[i]);

            }

Output:
0000000000000000000000000000000000001422

The first run outputs 1422 (it changes every time), but I need my program to keep taking different random #'s and adding it to the array until it's full (when it reaches 40). That's the problem I am having