/*
 * Program to check whether string is a palindrome.

 * Also illustrates using fgets to get a line of text, and strcmp to
 * compare strings.

 * With a command-line argument of "test", runs the function for some
 * predefined tests.  Otherwise prompts for a line of text.
 */
#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <ctype.h>

bool is_palindrome(char *s);
void testit(char *s);

int main(int argc, char *argv[]) {
	if ((argc > 1) && (strcmp(argv[1], "test") == 0)) {
		testit("aba");
		testit("");
		testit("abBA");
		testit("abcd");
		testit("A man, a plan, a canal -- Panama!");
		return 0;
	}

	char line[100];
	puts("enter a line of text");
	fgets(line, sizeof line, stdin);
	char *eol = strchr(line, '\n');
	if (eol == NULL) {
		puts("line too long");
	}
	else {
		*eol = '\0';
		printf("%s a palindrome\n", 
			is_palindrome(line) ? "is" : "is not");
	}
	return 0;
}

void testit(char *s) {
	printf("'%s' %s a palindrome\n", s, 
			is_palindrome(s) ? "is" : "is not");
}

bool is_palindrome(char *s) {
	char *p = s;
	char *q = s + strlen(s) - 1;
	while (p < q) {
		while (!isalpha(*p)) ++p;
		while (!isalpha(*q)) --q;
		if ((p < q) && (tolower(*p) != tolower(*q))) return false;
		++p; --q;
	}
	return true;
}