Calculate Array Sum Using Only Pointers

#include <stdio.h>

int calculate_sum(int *ptr, int n) {
    int *ptrnew=ptr;
    int sum;
    while(*ptrnew!=NULL){
    sum=sum+ *ptrnew;
    ptrnew++;
    }
    return sum;
}

int main() {
    int n;
    scanf("%d", &n);

    int arr[100];
    for (int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    int result = calculate_sum(arr, n);
    printf("%d", result);

    return 0;
}