错误：初始化程序不是常量

int isPalindrome(char *str)
{
    static int length = strlen(str);
    if (length < 1)
        return 1;
    if (str[0] == str[length - 1])
    {
        length -= 2;
        return isPalindrome(str + 1);
    }
    else return 0;
}

int main() {
    char word[25];
    printf("Please enter a word: ");
    scanf("%s", word);
    if (isPalindrome(word))
        printf("%s is Palindrome", word);
    else
        printf("%s isn't Palindrome", word);
    return 0;
}
int isPalindrome(char *str)
{
    static int le