int count = 0 ;
for(;;)
{
     // do xxxx on array element on every iteration
     xxxx(  array[count] ) ;

     if( count == N )
     {
         count = 0 ;

         // Do yyyy this every N iterations
         yyyy() ;
     }

     count++ ;
}

int count = 0 ;
for(;;)
{
     // Process whole array on every iteration
     for( int i = 0; i < sizeof(array)/sizeof(*array); i++ )
     {
         xxxx( array[count] ) ;
     }

     if( count == N )
     {
         count = 0 ;

         // Do yyyy this every N iterations
         yyyy() ;
     }

     count++ ;
}