"回文"是指顺读和反读内容都相同的字符串，如："ABCCBA"．这里引入两个指针变量，开始时，

分别指向字符串的首末字符，当两个指针所指字符相等时，两指针分别向前向后移一个字符位置，

并继续比较，直到两指针相遇．则说明该字符串是回文．若比较过程中，发现两字符不相等，则

可以判断该字符串不是回文．

代码如下：

/*判断字符串是否是回文*/

#include<stdio.h>
#define MAX 50
int cycle(char *s)
{
  char *h,*t;
  for(h=s,t=s+strlen(s)-1;t>h;h++,t--)
  {
    if(*h!=*t)
    {
        printf("%c",h);
        break;
    }
  }
  return t<=h;
}

main()
{
  char s[MAX];
  while(1)
  {
    puts("Please input the string you want to judge(input ^ to quit):");
    scanf("%s",s);
    if(s[0]=='^')
      break;
    if(cycle(s))
    printf("%s is a cycle string.\n",s);
    else
    printf("%s is not a cycle string.\n",s);
  }
  puts("\nThank you for you using ,bye bye!\n");
}

输出结果：

Please input the string you want to judge(input ^ to quit):
abcabc
 abcabc is not a cycle string.
Please input the string you want to judge(input ^ to quit):
abccba
abccba is a cycle string.
Please input the string you want to judge(input ^ to quit):