An array is cast to a pointer when passed as a parameter to a function

gistfile1.c

#include <stdio.h>

void initialize_array(int arr[], int val);

int main()
{
    int arr[30];

    initialize_array(arr, 5);

    int n = sizeof(arr) / sizeof(arr[0]);

    printf("n = %d\n", n);
    printf("sizeof(arr) = %lu\n", sizeof(arr));
    printf("sizeof(arr[0]) = %lu\n", sizeof(arr[0]));

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

    return 0;
}

void initialize_array(int arr[], int val)
{
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("n = %d\n", n);
    printf("sizeof(arr) = %lu\n", sizeof(arr));
    printf("sizeof(arr[0]) = %lu\n", sizeof(arr[0]));

    for (int i=0; i<n; i++)
    {
        arr[i] = val;
    }
}