#include <stdio.h>     /* C example */
#include <stdlib.h>    /* for atoi */

int main(int argc, char **argv)
{
	int n;         /* not initialized until line 15 */
	int i;         /* not initialized until line 17 */
	int sum = 0;   /* This initialization is wasted effort if argc != 2. */

	if (argc != 2) {
		fprintf(stderr, "%s: requires one command line argument\n", argv[0]);
		return EXIT_FAILURE;
	}

	n = atoi(argv[1]);

	for (i = 1; i <= n; ++i) {
		sum += i;   /* means sum = sum + i */
	}

	printf("The sum of the numbers from 1 to %d is %d.\n", n, sum);
	return EXIT_SUCCESS;
}