Programming in C

262 Chapter 11 Pointers
sets px to point n elements farther in the array, no matter what type of element is contained in
the array.
The increment and decrement operators ++ and -- are particularly handy when dealing
with pointers. Applying the increment operator to a pointer has the same effect as
adding one to the pointer, while applying the decrement operator has the same effect as
subtracting one from the pointer. So, if textPtr is defined as a char pointer and is set
pointing to the beginning of an array of chars called text, the statement
++textPtr;
sets textPtr pointing to the next character in text, which is text[1]. In a similar fashion,
the statement
--textPtr;
sets textPtr pointing to the previous character in text, assuming, of course, that
textPtr was not pointing to the beginning of text prior to the execution of this statement.
It is perfectly valid to compare two pointer variables in C.This is particularly useful
when comparing two pointers in the same array. For example, you can test the pointer
valuesPtr to see if it points past the end of an array containing 100 elements by comparing
it to a pointer to the last element in the array. So, the expression
valuesPtr > &values[99]
is TRUE (nonzero) if valuesPtr is pointing past the last element in the values array,
and is FALSE (zero) otherwise. Recall from previous discussions that you can replace the
preceding expression with its equivalent
valuesPtr > values + 99
because values used without a subscript is a pointer to the beginning of the values
array. (Remember, it’s the same as writing &values[0].)
Program 11.11 illustrates pointers to arrays.The arraySum function calculates the sum
of the elements contained in an array of integers.
Program 11.11 Working with Pointers to Arrays
// Function to sum the elements of an integer array
#include
int arraySum (int array[], const int n)
{
int sum = 0, *ptr;
int * const arrayEnd = array + n;
for ( ptr = array; ptr < arrayEnd; ++ptr )
sum += *ptr;