Question

I am trying to iterate through some number as 02100021, this is a routing number which needs to get validated if it is a proper routing number. Therefore I am using the ABA routing number validation check as 3*(d1+d4+d7) + 7*(d2+d5+d8) + (d3+d6+d9) where mod 10 = 0

Since I have the number in integer type, my first question is how can I iterate through such number with 0’s in it, or if there is some easier way of iterating through mode and multiplying it with such number.

Thanks

Answer 1

If I understand correctly, 7 * (d2, d5, d8) should be 7 * (d2 + d5 + d8).
Zeros modulo 10 do not count.

bool correct(long x) { 
    long a = x / 10 + x / 10000 + x / 10000000L;
    long b = x / 100 + x / 100000L + x / 100000000L;
    long c = x / 1000 + x / 1000000L + x / 1000000000L;
    int aba_checksum = (int)((3 * a + 7 * b + c) % 10);
    return aba_checksum == 0;
}

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Corrected for d[i] = digit * 10 ^ (9 – i)

bool correct(long x) { 
    long a = x / 100000000L + x / 100000L + x / 100;
    long b = x / 10000000L + x / 10000L + x / 10;
    long c = x / 1000000L + x / 1000L + x;
    int aba_checksum = (int)((3 * a + 7 * b + c) % 10);
    return aba_checksum == 0;
}

Modulo arithmetic can be done at the end.
To prevent overflow (to negative numbers) one might do it earlier, above even 7 * b does not overflow.