Problem with limiting inputs of char functions

Code:

#include <stdio.h>
#define MAX_INPUT_LENGTH 80

int is_palindrome(char []);

int main(void)
{
	int i = 0, indicator = 0;
	char words[MAX_INPUT_LENGTH] = {'a'};

	do
	{
		do
		{
			scanf("%c", &words[i]);
			
			i++;
		} while(words[i] != '\n');
		
		indicator += is_palindrome(words);

	} while(words[i] != '\n' && words[i-1] != '\n');

	return 0;
}

int is_palindrome(char arr[])
{
	int max, max_temp, i;

	for(i = 0; i < MAX_INPUT_LENGTH; i++)
	{
		if(arr[i] == '\n')
		{
			max = i - 1;
			max_temp = max;
			break;
		}
	}

	for(i = 0; i < max / 2 + 1; i++)
	{
		if(arr[i] != arr[max_temp])
			return 0;
		else
			max_temp--;
	}

	return 1;
}

Hi all, I am trying to input a few sentences and check if each sentence is a palindrome without the spaces, commas and other which means we only take into account of alphabets (a-z or A-Z) e.g.
A car, a man, a maraca.
A nut for a jar of tuna.
Are we not drawn onward to new era?

It should give output 3 e.g. the number of palindrome sentences entered.
A enter with nothing for the line will end it.

However, I am not sure how to filter out the spaces and other non-alphabets as inputs, plus my while statements which are aimed at ending inputs when there is an empty line does not seem to work but I felt that it would work. Anyone can explain to me why it does not work?

well from my understanding of your code you want the user to enter something along the lines
"text\n"
"\n"
and when 2 consecutive '\n's are found the loop should end, however, because you increment i after the 2nd '\n' is read you end up with

[\n] at i-2 and [\n] at i-1 and garbage at i

I want him to enter
"text\n"
"text\n"
"text\n"
"\n" // type this to exit
3 // output if all 3 sentences are palindromes

Originally Posted by hobolux

I want him to enter
"text\n"
"text\n"
"text\n"
"\n" // type this to exit
3 // output if all 3 sentences are palindromes

I see, the behavior would be the same, with the last two characters, both '\n', being located at i-2 and i-1, you are checking i-1 ('\n') and i (garbage), that is why the loop isn't stopping


edit: actually, the problem looks worse than that,

Code:

 do
        {
            scanf("%c", &words[i]);
            
            i++;
        } while(words[i] != '\n');

always checks garbage (the data is entered in words[0] and you check to see if words[1] contains '\n')