/*
 * Version of whilesum.c that reads from file not stdin and writes
 * partial sums to output file (mostly useful as an illustration of
 * fprintf).
 *
 * Filenames are specified with command-line arguments.
 */
#include <stdio.h>
#include <stdlib.h>

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

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