15.8.c

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

#define MAXLINE 1024

int main(void)
{
    int     n, int1, int2;
    char    line[MAXLINE];

    while ((n = read(STDIN_FILENO, line, MAXLINE))) {
        line[n] = 0;
        if (sscanf(line, "%d%d", &int1, &int2) == 2) {
            sprintf(line, "%d\n", int1 + int2);
            n = strlen(line);
            if (write(STDOUT_FILENO, line, n) != n) {
                printf("write error\n");
                exit(-1);
            }
        } else {
            if (write(STDOUT_FILENO, "invalid args\n", 13) != 13) {
                printf("write error\n");
                exit(-1);
            }
        }
    }

    return 0;
}