is_palindrome_test.c

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

/* returns: non-zero if s points to a sequence
 * of characters that is palindromic, 0 if not
 */
int is_palindrome (char *s) {

	int N, n;
	int i;

	N = strlen(s) - 1;

	n = N - 1 / 2;

	if (n < 0) {
		return 0;
	}

	for (i = 0; i <= n; i++) {
		if (s[i] != s[N - i]) {
			return 0;
		}
	}

	return 1;
}

#ifndef NO_TEST

struct unit {
	char *s;
	int r;		
};

static struct unit tests[] = {
	{ "racecar",  1 },
	{ "racecars", 0 },
	{ "aabcc",    0 },
	{ "aabbaa",   1 },
	{ "a",        1 },
	{ "aa",       1 },
	{ "aba",      1 },
	{ "abba",     1 },
	{ "abcba",    1 },
	{ "",         0 },
};

int main () {

	int i, r;

	for (i = 0; i < sizeof tests / sizeof tests[0]; i++) {
		r = is_palindrome(tests[i].s);

		if (r != tests[i].r) {
			fprintf(stderr, "%d: FAILED: expected is_palindrome(%s) == %d, got %d\n",
				i + 1, tests[i].s, tests[i].r, r);
			exit(EXIT_FAILURE);
		}
	}

	puts("PASSED");
	exit(EXIT_SUCCESS);
}

#endif /* NO_TEST */