C Pointers and Arrays
Arrays and pointers are closely related in C: the name of an array can decay into a pointer to its first element in most expressions. This lets you use pointer arithmetic to move through array elements.
Understanding this relationship helps explain why array indexing like arr[i] is essentially equivalent to *(arr + i).
int *p = arr;
*(p + i) == arr[i]Array-to-pointer decay
When an array name is used in most expressions, it decays into a pointer to its first element. So `int *p = arr;` makes p point to arr[0] without needing &.
Pointer arithmetic
Adding an integer to a pointer moves it forward by that many elements (not bytes), based on the pointed-to type's size. `*(p + 1)` accesses the second element.
#include <stdio.h>
int main() {
int arr[3] = {10, 20, 30};
int *p = arr;
printf("%d\n", *(p + 1));
return 0;
}20p points to arr[0], so *(p + 1) accesses arr[1], which is 20.
#include <stdio.h>
int main() {
int arr[3] = {1, 2, 3};
int *p = arr;
for (int i = 0; i < 3; i++) {
printf("%d ", *(p + i));
}
printf("\n");
return 0;
}1 2 3 Pointer arithmetic can traverse an array just like index-based access.
Key points
- An array name decays into a pointer to its first element.
- Pointer arithmetic advances by element size, not raw bytes.
- arr[i] and *(arr + i) are equivalent expressions.
- Arrays and pointers are related but not identical: sizeof behaves differently on each.