/* 
 * program to sum integers from standard input 
 */
#include <stdio.h>

int sum_input(void);

int main(void) {
    printf("enter some integers, anything else to stop\n");
    int n = sum_input();
    printf("sum is %d\n", n);
    return 0;
}

/* 
 * read integers from stdin until non-integer found
 * returns sum
 */
int sum_input(void) {
    int n;
    if (scanf("%d", &n) == 1) {
        return n + sum_input();
    }
    else {
        return 0;
    }
}