/*
 * Version of whilesum.c that reads from file and writes partial sums
 * to output file.
 *
 * Command-line arguments:
 * input file
 * output file
 */
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char* argv[]) {
	if (argc != 3) { 
		fprintf(stderr, "usage:  %s infile outfile\n", argv[0]);
		return EXIT_FAILURE;
	}
	FILE * infile = fopen(argv[1], "r");
	if (infile == NULL) { 
		fprintf(stderr, "cannot open file %s\n", argv[1]);
		return EXIT_FAILURE; 
	}
	FILE * outfile = fopen(argv[2], "w");
	if (outfile == NULL) { 
		fprintf(stderr, "cannot open file %s\n", argv[2]);
		return EXIT_FAILURE; 
	}

	int sum = 0;
	int n;
	/* slightly cryptic but C-idiomatic .... */
	while (fscanf(infile, "%d", &n) == 1) {
		sum += n;
		fprintf(outfile, "partial sum %d\n", sum);
        /* uncomment to see feof() return value 
        printf("eof on infile?  %c\n", feof(infile) ? 'y' : 'n');
        */
	}
	/* check whether loop stopped because of EOF or error */
	if (!feof(infile)) {
		fprintf(stderr, "bad input\n");
		fclose(infile);
		fclose(outfile);
		return EXIT_FAILURE;
	}
	printf("sum %d\n", sum);
	fclose(infile);
	fclose(outfile);
	return EXIT_SUCCESS;
}