Cycling through an array

[Allessandro]

I know that if we want to cycle through an array (going from end to the starting) we can use "%" operator.Bu what must I do if I want to cycle in the opposite direction.For example if i have an array with 5 elements (array[5]) and when i have -2 in hand, i want to rearrange this number and i want to access to array[4] of the array.
Thanks

[itsme86]

% doesn't seem like it would be a great operator to use for cycling through an array. Do you actually mean something besides cycling? Your question is pretty unclear (e.g. what does "-2 in hand" mean?) The common operators for cycling through an array are -- for end to start, and ++ for start to end.

[Allessandro]

When you have an array of 5 elements and in your program and if you want to cycle through your array, don't you use "%" operator.For example if you have 6 and array[6%5]--> array[1] so that you will be still in the bounds.I want to do the reverse.If i have -1, i want to rearrange the number so that i can use this number to access array[5]...

[itsme86]

How about: array[5 - (abs(-1) % 5)]?
Or more generally: array[array_size - (abs(index) % array_size)]

For -1 you get 4.
For -2 you get 3.
For -3 you get 2.
For -4 you get 1.
For -5 you get 0.
For -6 you get 4.
and so on...

[Dave_Sinkula]

#include <stdio.h>
#include <stdlib.h>

void foo(const int *array, int size, int index)
{
   int i = index % size;
   if ( i < 0 )
   {
      i += size;
   }
   printf("%2d: array[%d] = %d\n", index, i, array[i]);
}

int main(void)
{
   const int value[] = {10,20,30,40,50,60};
   int i;
   for ( i = -8; i < 8; ++i )
   {
      foo(value, sizeof value / sizeof *value, i);
   }
   return 0;
}

/* my output
-7: array[5] = 60
-6: array[0] = 10
-5: array[1] = 20
-4: array[2] = 30
-3: array[3] = 40
-2: array[4] = 50
-1: array[5] = 60
 0: array[0] = 10
 1: array[1] = 20
 2: array[2] = 30
 3: array[3] = 40
 4: array[4] = 50
 5: array[5] = 60
 6: array[0] = 10
 7: array[1] = 20
*/