How to pass arrays to functions in C

main.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int sum(int* arr, int n) {
    int i, s = 0;
    arr[0] = 10;
    for (i = 0; i < n; i++) {
        s += arr[i];
    }
    printf("Size from sum function: %llu\n", sizeof(arr));
    return s;
}

int main(int argc, char* argv[]) {
    int arr[] = { 1, 2, 3, 4, 5, 6, 7 };
    int s = sum(arr, 7);
    printf("Sum: %d\n", s);
    printf("First element: %d\n", arr[0]);
    printf("Size: %llu\n", sizeof(arr));
    
    return 0;
}