C program that reads in a string and checks if it is a palindrome

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

int main()
{
    char str[100];
    int i, j, len;

    printf("Enter a string: ");
    gets(str);

    // Remove whitespace and punctuation from the string
    for (i = 0, j = 0; str[i] != '\0'; i++)
    {
        if (isalpha(str[i]))
        {
            str[j] = tolower(str[i]);
            j++;
        }
    }
    str[j] = '\0';

    len = j;

    // Check if the string is a palindrome
    for (i = 0, j = len - 1; i < len / 2; i++, j--)
    {
        if (str[i] != str[j])
        {
            printf("%s is not a palindrome\n", str);
            return 0;
        }
    }

    printf("%s is a palindrome\n", str);

    return 0;
}