remove punctuation in C

[siddharth29]

/*Write a program of palindrome using stack [implement stack using array]:
Note: Punctuation, Capitalization, and Spaces are ignored. For Example- Poor dan is in a droop.

Date : February 21,2014 */

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

bool is_palindrome(const char* s)
{
    int i = 0;
    int j = strlen(s) - 1;
    while(j >= 0)
    {
        if(!isalpha(s[i]))
        {
            ++i;
        }
        else if(!isalpha(s[j]))
        {
            --j;
        }
        else if(tolower(s[i]) != tolower(s[j]))
        {
            return false;
        }
        ++i;
        --j;
    }
    return true;
}


void printme(const char* s)
{
    printf(" \" %s\" ",s);
    if(is_palindrome(s))
    {
        printf(" IS a palindrome! \n");
    }
    else
    {
        printf(" IS NOT a palindrome! \n");
    }
}

int main()
{
    char s[] = "kajak";
    char s2[] = "Poor Dan is in a droop";
    char s3[] = "not a palindrome";

    printme(s);
    printme(s2);
    printme(s3);
    return 0;
}