#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <ctype.h>

int main(int argc, char **argv) {
	if (argc <= 1) {
		fprintf(stderr, "usage: %s [ul]\n", argv[0]);
		exit(EXIT_FAILURE);
	}

	char *mode = argv[1];
	bool upper;
	switch (mode[0]) {
	case 'u':
		upper = true;
		break;
	case 'l':
		upper = false;
		break;
	default:
		fprintf(stderr, "usage: %s [ul]\n", argv[0]);
		exit(EXIT_FAILURE);
	}	

	int c;
	while ((c = fgetc(stdin)) != EOF) {
		if (upper) 
			putc(toupper(c), stdout);
		else
			putc(tolower(c), stdout);
	}
	if (ferror(stdin)) {
		fprintf(stderr, "oops\n");
		exit(EXIT_FAILURE);
	}
}