请高手指点一下

 

#include <iostream> #include <string>

using namespace std;

int main()

{     char a[1002],b[1002],i;  

   while(gets(a))  

   {        if(strcmp(a,"START")==0) memset(b,0,sizeof(b));    

else if(strcmp(a,"END")==0)printf("%s/n",b);    

else if(strcmp(a,"ENDOFINPUT")==0) break;    

else     {        for(i=0;a[i]='\0';i++)   

    {         if(a[i]>='A'&&a[i]<='Z')  

  {          if(a[i]+21>90)          b[i]=a[i]-5;       

   else          b[i]=(a[i]+21);    }                                          

     else                b[i]=a[i];}           

   }                           

   }         return EXIT_SUCCESS; }