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Pointers and arrays

July 28th, 2010 c# No comments

The concept of array is very much bound to the one of pointer. In fact, the identifier of an array is equivalent to the address of its first element, as a pointer is equivalent to the address of the first element that it points to, so in fact they are the same concept. For example, supposing these two declarations:
int numbers [20];
int * p;
The following assignment operation would be valid:
p = numbers;

After that, p and numbers would be equivalent and would have the same properties. The only difference is that we could change the value of pointer p by another one, whereas numbers will always point to the first of the 20 elements of type int with which it was defined. Therefore, unlike p, which is an ordinary pointer, numbers is an array, and an array can be considered a constant pointer. Therefore, the following allocation would not be valid:

numbers = p;
Because numbers is an array, so it operates as a constant pointer, and we cannot assign values to constants.

Due to the characteristics of variables, all expressions that include pointers in the following example are perfectly valid:

// more pointers
#include
using namespace std;

int main ()
{
int numbers[5];
int * p;
p = numbers; *p = 10;
p++; *p = 20;
p = &numbers[2]; *p = 30;
p = numbers + 3; *p = 40;
p = numbers; *(p+4) = 50;
for (int n=0; n<5; n++)
cout << numbers[n] << ", ";
return 0;
}

output:
10, 20, 30, 40, 50,