Pointers and Arrays

Pointers and Arrays

In C, arrays and pointers are closely related. An array name, in most contexts, decays to a pointer to its first element.

Array Decay

int arr[5] = {10, 20, 30, 40, 50};
int *p = arr;   // arr decays to &arr[0]

Now p[i] and arr[i] access the same memory. You can use pointer arithmetic or array indexing interchangeably:

printf("%d\n", p[2]);     // 30
printf("%d\n", *(p + 2)); // 30 (same thing)

Tractor beam arrays: multiple beams working in concert, each pointing to a different target. That's pointer arithmetic in action.

Arrays as Function Parameters

When you pass an array to a function, it decays to a pointer. The function receives a pointer, not a copy:

void print_array(int *arr, int len) {
    for (int i = 0; i < len; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main() {
    int nums[] = {1, 2, 3};
    print_array(nums, 3);
}

Modifying Arrays Through Pointers

Since the function gets a pointer to the original array, it can modify the array:

void double_elements(int *arr, int len) {
    for (int i = 0; i < len; i++) {
        arr[i] = arr[i] * 2;
    }
}

Your Task

Write a function void reverse(int *arr, int len) that reverses an array in place. Call it on {1, 2, 3, 4, 5} and print each element separated by spaces.