15.4.3.c

#include "apue.h"

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

  while (fgets(line, MAXLINE, stdin) != NULL) {
    if (sscanf(line, "%d%d", &int1, &int2) == 2) {
      if (printf("%d\n", int1 + int2) == EOF) {
        err_sys("printf error");
      }
    } else {
      if (printf("invalid args\n") == EOF) {
        err_sys("printf error");
      }
    }
  }
  exit(0);
}