how to iterate all array element starting from a random index.

Question

I was wondering if is it possible to iterate trough all arrays elements starting from any of its elements without pre-sorting the array.

just to be clearer suppose i have the array of 5 elements:

0 1 2 3 4

i want to read all elements starting from one of their index like:

2 3 4 0 1

or

4 0 1 2 3

the idea is to keep the element order in this way:

n ,n+1 ,..., end ,start, ..., n-1

One solution could be (pseudocode):

int startElement;
int value;
for(startElement;startElement<array.count;startElement++){
  value = array[startElement];
}
for(int n = 0; n<startElement;n++){
  value = array[n];
}

but I don't know if there's a better one. Any suggestions?

Answer 1

Use the modulus operator:

int start = 3;
for (int i = 0; i < count; i++)
{
    value = array[(start + i) % count];
}

Answer 2

Yes it's possible. You need to use a psuedorandom number picker like rand() or arc4rand() though. Something like:

int arrayElement = arc4rand() % 5; // picks a number 0 to 4
for (int i = 0; i < 5; i++)
{
    if (arrayElement > 4)
    {
        arrayElement -= 5; // after element 4 go back to zero
    }
    someValue = yourArray[arrayElement];
}