//测试文本是否回环
#include<iostream.h>
#define SIZE=30;
main()
{
      char words[30],words1[30];
      int ctr,ctr1,ctr2;
      ctr2=0;
      cout<<"请输入需要鉴别的语句：\n";
      gets(words);
      puts(words);
      for(ctr1=0;ctr1<30;ctr1++)
      {
                if((words[ctr1]>64&&words[ctr1]<91)||(words[ctr1]>96&&words[ctr1]<123))
                {
                words1[ctr2]=words[ctr1];
                words1[ctr2+1]='\0';
                ctr2++ ;}
                else{continue;}
               

      cout<<words1<<"\n"<<ctr2;
      }
      words1[ctr2]='\0';
      ctr2--;
      for(ctr=0;ctr<=ctr2;ctr++)
      {words1[ctr]=words1[ctr]&223;}
      cout<<"处理后语句为："<<words1<<"\n";
      cout<<ctr2;
      
      ctr=0;
      while(words1[ctr]==words1[ctr2-ctr])
      {ctr++;}
      ctr2++;
      if (ctr==ctr2)
      {cout<<"这是一个回环语句。\n";}
      else
      {cout<<"这不是一个回环语句。\n";}
      cout<<ctr;
      cin.get();
      return 0;
      }
" border="0" />

请输入需要鉴别的语句：
iamai
iamai
i
1ia
2iam
3iama
4iamai
5iamaip
6iamaipX
7iamaipXP
8处理后语句为：IAMAIPXP
7这不是一个回环语句。
0

为什么words1赋值中会出来莫名其妙的pXP？

出现非法字串的原因可以肯定是你访问了非法的地址,极有可能出现非法字符

内存分配问题，你需要动态分配内存！

//测试文本是否回环
#include<iostream>

using namespace std;
 
const int SIZE=30;//比define要好
int main()
{
      char *words= new char [SIZE];//动态分配！
      char words1[SIZE];
      int ctr,ctr1,ctr2;
      ctr2=0;
      cout<<"请输入需要鉴别的语句:\n";
      gets(words);
      puts(words);
      int len=sizeof(words)/sizeof(char);//数组的长度，也就是字符串的长度！
      for(ctr1=0;ctr1<=len;ctr1++)
      {
                if((words[ctr1]>='a'&&words[ctr1]<='z')||(words[ctr1]>='A'&&words[ctr1]<='Z'))
                {
                    words1[ctr2]=words[ctr1];
                    words1[ctr2+1]='\0';
                    ++ctr2;
                }
                else
                   continue;
               cout<<words1<<"\n"<<ctr2;
      }
      delete [] words;//释放内存！
      words1[ctr2]='\0';
      ctr2--;
      for(ctr=0;ctr<=ctr2;ctr++)
          words1[ctr]=words1[ctr]&223;//
      cout<<"处理后语句为："<<words1<<"\n";
      cout<<ctr2;
      ctr=0;
      while(words1[ctr]==words1[ctr2-ctr])
          ctr++;
      ctr2++;
      if (ctr==ctr2)
        cout<<"这是一个回环语句。\n";
      else
        cout<<"这不是一个回环语句。\n";
        cout<<ctr;
      system("pause");
      return 0;   
}

比如说iam ai，赋值给words1到iam就停止了，'/0'之后无法判断了