【NOIP】提高组2012 vigenere密码

#include<cstdio>
#include<cstring>
const int maxm=1010;
char sm[maxm],key[maxm],s[maxm];
int len,lenk;
bool isbig(char c)
{return c>=‘A‘&&c<=‘Z‘;}
int main()
{
    scanf("%s",key);scanf("%s",sm);
    len=strlen(sm);lenk=strlen(key);
    for(int i=lenk;i<len;i++)key[i]=key[i%lenk];
    for(int i=0;i<len;i++)
     {
         int a=isbig(sm[i])?sm[i]-‘A‘:sm[i]-‘a‘;
         int b=isbig(key[i])?key[i]-‘A‘:key[i]-‘a‘;
         if(a<b)a+=26;
         s[i]=isbig(sm[i])?(a-b)+‘A‘:(a-b)+‘a‘;
     }
    printf("%s",s);
    return 0;
}