// TODO: Implement populate_array
/*
 * Convert a 9 digit int to a 9 element int array.
 */
int populate_array(int sin, int *sin_array) {

    int count; // keeps track of the number of digits so far
    int quotient; // result after /
    int remainder; // result after %
    int curr_index = 0; // curr index for the remainder to be inserted

    // add the digit of sin to the empty array
    while (sin != 0 && count < 10){
        count += 1;
        quotient = sin / 10;
        remainder = sin % 10;
        sin_array[curr_index] = remainder;
        curr_index += 1;
    }

    // check if count is 9 and return 1 / 0
    if (count == 9){
        return 0;
    }
    else{
        return 1;
    }
    // flip the array to get the sin inputted


}

// TODO: Implement check_sin
/*
 * Return 0 if the given sin_array is a valid SIN, and 1 otherwise.
 */
int check_sin(int *sin_array) {
    
    // sin starts with zero makes SIN # invalid
    if (sin_array[0] == 0){
        return 1;
    }
    else{
        int sum = 0, nDigits = 9;
    int isSecond = 0;
    for (int i = nDigits - 1 ; i >=0 ; i --){
       int d = sin_array[i] - '0';

       if (isSecond == 1){
        d = d * 2;
       }
       sum += d / 10;
       sum += d % 10;

       if (isSecond == 0){
        isSecond = 1;
       }
       else{
        isSecond = 0;
       }
        
    }
    if (sum % 10 == 0){ // the total should add to a number divisible by 10
        return 0;
    }
    else{
        return 1;

    }


    }
    

}

int main(int argc, char **argv) {
    // TODO: Verify that command line arguments are valid.
     if (argc < 2 || argc > 2){
        return 2;
    }
    else{
        int sin_number = strtol(argv[1], NULL, 10);
        int array[9];

        if ((populate_array(sin_number, array) | check_sin(array)) == 1){
        printf("Invalid SIN \n");
        return 1;
        }

        else{
             printf("Valid SIN\n");
    // TODO: Parse arguments and then call the two helpers in sin_helpers.c
    // to verify the SIN given as a command line argument.

   
        return 0;
    }
    
    
    }
}
Intended behavior: why is my main not running? I get an error saying implicit declaration of helper function
