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

extern int sum(const int *a, int n);  /* Prototype of function */

int main(void) {
    int *a;
    int n, s, i;
    while (1) {
        printf("Enter the length n of array: ");
        if (scanf("%d", &n) < 1 || n <= 0)
            break;
        a = (int *) malloc(n*sizeof(int));
        printf("Enter elements of array:\n");
        for (i = 0; i < n; ++i) {
            if (scanf("%d", &(a[i])) < 1)
                exit(-1);
        }
        s = sum(a, n);    
        printf("sum = %d\n", s);
        free(a);
    }
    return 0;
}