#include <stdio.h>
# include<iostream.h>
void main()
{
char M[100];
char C[100];
int k,i;
cout<<"\n***加密***\n"<<endl;
cout<<"请输入明文M(注意不要输入空白串)"<<endl;
gets(M);
cout<<"请输入您的密钥(必需是整数):"<<endl;
cin>>k;
for(i=0;M[i]!='\0';i++)
C[i]=(M[i]-'a'+k)%26+'a';
C[i]='\0';
cout<<"所得的凯撒密码为:"<<endl;
cout<<C<<endl;
cout<<"\n***解密***\n"<<endl;
cout<<"您的凯撒密码:"<<C<<endl;
cout<<"你的密钥是："<<k<<endl;
for(i=0;C[i]!='\0';i++)
M[i]=(C[i]-'a'-k+26*(k/26+1))%26+'a';
M[i]='\0';
cout<<"你的明文为:"<<M<<endl;
}
