Array name as pointer
- C course
- Beginner
- Lesson 77/116
- 5 min
Learn that the array name is a pointer to the first element.
Array name as pointer
In C an array name decays into the address of its first element. So you can assign an array name directly to a pointer.
int arr[3] = {10, 20, 30};
int *p = arr; /* p holds the address of arr[0] */
printf("%d", *p); /* prints 10 */This is called array decay: the array info drops to a pointer. arr and p now refer to the same memory region.
Array decay in functions
When you pass an array to a function the array name decays into a pointer. The function sees the array itself, not a copy. So the function can modify the array elements.
void add_one(int *arr, int n) {
for (int i = 0; i < n; i++) arr[i]++;
}The array length is not stored in the pointer; you must pass the size as a separate parameter.
Practice Access array elements via pointer
Define int arr[3] = {10, 20, 30};. Bind p to arr with int *p = arr;. With three printf calls print *p, *(p + 1) and *(p + 2) on separate lines. Output should be 10, 20, 30.
Starter code
#include <stdio.h>
int main(void) {
int arr[3] = {10, 20, 30};
/* bind p to arr; print *p, *(p+1), *(p+2) */
return 0;
}Sample solution
#include <stdio.h>
int main(void) {
int arr[3] = {10, 20, 30};
int *p = arr;
printf("%d\n", *p);
printf("%d\n", *(p + 1));
printf("%d\n", *(p + 2));
return 0;
}Expected output
10 20 30
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 int arr[3] = {10,20,30}; printf("%d", *(arr+1)); prints what?
- 10
- 20 Correct answer
- 30
- 11
Explanation: *(arr+1) is arr[1], which is 20.
2 Assign array to pointer
int arr[3] = {10, 20, 30};
int *p = ____; /* p now points to arr */int arr[3] = {10, 20, 30};
int *p = arr; /* p now points to arr */Explanation: You can assign an array name directly to a pointer.
3 Match array-pointer concepts
| Term | Meaning |
|---|---|
arr |
address of first element |
arr+1 |
address of second element |
*(arr+2) |
value of third element |
int *p = arr |
pointer assignment |