/*
 * Program to add numbers.
 *
 * Input and output from files, names given by command-line arguments.
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[]) {

	int input;
	int sum = 0;

    FILE *infile;
    FILE *outfile;

    if (argc < 3) {
        fprintf(stderr, "usage:  %s infile outfile\n", argv[0]);
        return EXIT_FAILURE;
    }

    if (strcmp(argv[1], argv[2]) == 0) {
        fprintf(stderr, "error:  input and output file are the same\n");
        return EXIT_FAILURE;
    }

    infile = fopen(argv[1], "rb");
    if (infile == NULL) {
        fprintf(stderr, "unable to open input file %s\n", argv[1]);
        return EXIT_FAILURE;
    }

    outfile = fopen(argv[2], "wb");
    if (outfile == NULL) {
        fprintf(stderr, "unable to open output file %s\n", argv[2]);
        return EXIT_FAILURE;
    }

	while (fscanf(infile, "%d", &input) == 1) {
		sum += input;
	}
	fprintf(outfile, "result is %d\n", sum);

    fclose(infile);
    fclose(outfile);

	return EXIT_SUCCESS;
}