Simple checksum algorithm

Question

Array a of ints contains the digits of a number. For this example I'll insert random numbers but the code must work for any set of numbers. I have to add together the ints in the array and then store the last digit in that sum into a variable called checksum.

In this example, 3 + 5 + 7 = 15 so checksum would = 5. Here's my code so far. How would I go about calculating the checksum?

int[] a = { 3, 5, 7 }; 

int checksum = 0;
int i = 0;

while ( i < a.length )
    {
        checksum += a[i];
        i++;
    }

checksum = ???????;

Are you looking for this? http://stackoverflow.com/questions/2609315/recognizing-when-to-use-the-mod-operator — irrelephant, Oct 26 '12 at 02:04

score 2 · Answer 1 · answered Oct 26 '12 at 02:04

2

Simply use the modulus operator. checksum %= 10

This basically means, set checksum to the remainder of checksum/10 which happens to be the last digit.

Edit:

Just to offer another suggestion, your while loop is really better suited to be a for-each loop, just try:

for(int i : a){
    checksum += i;
}

Read it as "Forint i in a". IMHO this is slightly more understandable and you avoid some typing.

answered Oct 26 '12 at 02:04

daniel gratzer

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don`t you mean checksum %= a.length ? – ılǝ Oct 26 '12 at 02:07
@ile No, check the example given above, he wants the last digit. – daniel gratzer Oct 26 '12 at 02:09
Sorry, I confused checksum with average value. However, I still think your answer is wrong. If the values were 1, 3, 7 , %= will return 1, whereas it should be 3, if I understood correctly - "store the last number in that sum into a variable called checksum" – ılǝ Oct 26 '12 at 02:16
`3 + 5 + 7 = 15 so checksum would = 5` 3+5+7= 15, the last digit of which is 5, or 15%10. – daniel gratzer Oct 26 '12 at 02:20
The question states: "the code must work for any set of numbers." – ılǝ Oct 26 '12 at 02:24
Yes, and so does the code above, the last digit of number, n, is always n%10. Can you please explain what your question is? – daniel gratzer Oct 26 '12 at 02:26
Do you mean "digit", not number? I think this is the source of the misunderstanding. – ılǝ Oct 26 '12 at 02:29
I'm just going off the question which uses the somewhat confusing term `number` but the example makes it clear that he means `digit`. Im editing to remove the ambuigity – daniel gratzer Oct 26 '12 at 02:31
You are right, I had been thinking of "last but one" number, which was still 5. – ılǝ Oct 26 '12 at 02:34
Well, the `for each` is kinda slower than a true for with indexes, so he may want to use a normal for with a large amounts of data. – Javier Diaz Oct 26 '12 at 08:14
Thats true, I just suggested it as an after thought @JavierDiaz – daniel gratzer Oct 26 '12 at 18:24

Simple checksum algorithm

1 Answers1