#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void reverse(char *s) {
	for (char *front = s, *back=s+strlen(s)-1; front < back; *front ^= *back, *back ^= *front, *front ^= *back, ++front, --back) {}
}

void test(const char* s) {
	char* tmp = strdup(s);
	printf("before: %s\n", tmp);
	reverse(tmp);
	printf("after: %s\n\n", tmp);
	free(tmp);
}

int main(int argc, char** argv) {
	test("hello, dingus");
	test("hello, dingus!");
	test("");
}