/*
 * Version of loop-sum.c that reads from file not stdin.
 * Filename is specified with command-line argument.
 */
#include <stdio.h>
#include <stdlib.h> /* has EXIT_SUCCESS, EXIT_FAILURE */

int main(int argc, char* argv[]) {
	if (argc < 2) { 
		printf("usage:  %s filename\n", argv[0]);
		return EXIT_FAILURE; 
	}
	FILE * infile = fopen(argv[1], "r");
	if (infile == NULL) { 
		printf("cannot open file %s\n", argv[1]);
		return EXIT_FAILURE; 
	}

	int n;
	int sum = 0;
	/* slightly cryptic but C-idiomatic .... */
	while (fscanf(infile, "%d", &n) == 1) {
		sum +=n;
	}
	/* check whether loop stopped because of EOF or error */
	if (feof(infile)) {
		/* normal EOF */
		fclose(infile);
		printf("sum %d\n", sum);
		return EXIT_SUCCESS;
	}
	else {
		/* error */
		printf("invalid input\n");
		fclose(infile);
		return EXIT_FAILURE;
	}
}