判斷一字符串是否爲迴文，是返回1，不是返回0，出錯返回-1

#include <stdio.h>

int fun(char *p)
{
if (p == NULL)
return -1;

char *pstart = p;
char *pend   = p;

while (*pend)
{
pend++;
}
pend--;

while (pstart < pend)
{
if (*pstart != *pend)
return 0;

pstart ++;
pend --;
}

return 1;
}


int main()
{
char *p = "abcdefgfedcba";

printf ("%d\n", fun(p));

return 0;
}