C - when to use pointer arithmetic, when to use array indexing?

Question

In C, when is it preferrable to use one over the other?

Answer 1

in according to MISRA C++ 2008 (Rule 5-0-15): Array indexing shall be the only form of pointer arithmetic.

but this rule has an exception:

The increment/decrement operators may be used on iterators implemented by pointers to an array

template < typename IterType > 
uint8_t sum_values ( IterType iter, IterType end ) 
{ 
    uint8_t result = 0;
    while ( iter != end ) 
    { 
        result += *iter; 
        ++iter;              // Compliant by exception 
    }
    return result; 
}
void my_fn ( uint8_t * p1, uint8_t p2[ ] ) 
{ 
    uint8_t index = 0; 
    uint8_t * p3; 
    uint8_t * p4;
    *p1 = 0; 
    ++index; 
    index = index + 5;
    p1      = p1 + 5;     // Non-compliant – pointer increment 
    p1[ 5 ] = 0;          // Non-compliant – p1 was not declared as array 
    p3      = &p1[ 5 ];   // Non-compliant – p1 was not declared as array
    p2[ 0 ]     = 0; 
    p2[ index ] = 0;          // Compliant 
    p4          = &p2[ 5 ];   // Compliant 
}
uint8_t a1[ 16 ]; 
uint8_t a2[ 16 ];
my_fn ( a1, a2 ); 
my_fn ( &a1[ 4 ], &a2[ 4 ] );
uint8_t a[ 10 ]; 
uint8_t * p;
p          = a; 
*( p + 5 ) = 0;   // Non-compliant 
p[ 5 ]     = 0;   // Compliant
sum_values ( &a1[ 0 ], &a1[ 16 ] );