How can I access the first element of an array after executing in a loop?

Question

I want to access the first array element after a loop completes executing.

I have an array that stores some numbers like 1,2,3,4,5. The array is always initialized with index 0 but I'm not using 0th index to store anything.

So what I want is using indexes in ring fashion like 1-2-3-4-5-1 I can achieve this if I use array from 0th index like 0-1-2-3-4-0 with modulus operation.

How can do that when my array index starts from 1 instead?

Why are you not using the 0th element? This will lead to a lot of struggle and extra effort and a huge bug potency. If 0-based indexing is something you can't get used to, then C++ is not for you. If you just feel you can't get used to it, then believe me, you will. — Sebastian Mach
– Sebastian Mach, Commented Apr 23, 2012 at 15:55
@phresnel : well, the reason is array store Node numbers. Nodes are started from 1-N numbered with array indexes. Nodes are nothing but processors. I don't want to -1 each time I use it. It's difficult to read as well. And this is C — SachinGutte
– SachinGutte, Commented Apr 23, 2012 at 16:00
@phresnel : Maybe you don't understand the scenario. I've a structure array with 2 variables. These two variables are regarding processor identity number/priority and it's status. If I don't number processors with their index values then I have to use 3rd variable in structure for number. That will consume more space than keeping 0 index of structure empty. What bug potency you're talking about ?? If you address something then you should clarify it as well. That would have been more helpful than your comments. — SachinGutte
– SachinGutte, Commented Apr 23, 2012 at 16:17
@phazorRise by bug potency (potential) he means that if other people (or your future self) use your code, they will expect array indices to be 0 based and will try to use the 0th element, creating a bug. — Seth Carnegie
– Seth Carnegie, Commented Apr 23, 2012 at 16:19
@SethCarnegie : That's right but for above mentioned scenario I felt it to be started from 1 position. And by looking at code and comments anyone can understand the reason behind it. That's what I thought. But if still I'm wrong maybe I should use 0 index as well and avoid a little trouble and fall in another. — SachinGutte
– SachinGutte, Commented Apr 23, 2012 at 16:25

Sergey Kalinichenko · Accepted Answer · 2012-04-23 15:54:22Z

You can subtract one, do %, and add one back:

a[((i-1)%ARRAY_LEN)+1]

This illustrates a problem of fighting the convention: instead of a simple % operation, you need a subtraction, a %, and an addition. Tather than fighting the C/C++ convention, it's best to embrace it for more efficiency and readability by others.

unwind · Accepted Answer · 2012-04-23 15:54:39Z

3

Well ... You can just use logic instead of modulo when you increase the index:

if (++index >= 6) index = 1;

answered Apr 23, 2012 at 15:54

unwind

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1 Comment

ouah Over a year ago

in the embedded world this has the strong advantage over the % solution to not require a division.

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