C++实现单置换密码

#include<iostream>
#include<string>
#include<fstream>
using namespace std;

ifstream in("密码学.txt");

void JiaMi(char ZhiHuan[]);   //加密函数
void JieMi(char ZhiHuan[]);   //解密函数
void setZhiHuan(char ZhiHuan[],char fanZhiHuanBiao[]);  //设置置换表函数
int main()
{
 int m;    //确定是加密或解密？加密为1，解密为2
 char ZhiHuanBiao['z'+1];   //正向置换表，加密时用
 char fanZhiHuanBiao['Z'+1];  //反向置换表，解密时用
 cout<<"加密按输入1，解密输入2"<<endl;
 in>>m;    //读入m
 setZhiHuan(ZhiHuanBiao, fanZhiHuanBiao); //设置置换表
 switch(m) //判断m值，执行相应的功能
 {
 case 1: JiaMi(ZhiHuanBiao);break;
 case 2: JieMi(fanZhiHuanBiao);break;
 default:break;
 }
 return 0;
}

void JiaMi(char ZhiHuan[]) //加密
{
 string MingWen;  //保存明文
 cout<<endl<<"请输入明文：";
 getline(in,MingWen); //读入明文
 cout<<MingWen<<endl;  
 cout<<"加密后的密文为："<<endl;
 for(int i=0; i<MingWen.length(); i++) //直接利用置换表输出密文
 {
 if(MingWen[i]>='a' && MingWen[i]<='z')
 cout<<ZhiHuan[ MingWen[i] ];
 else cout<<MingWen[i];
 }
 cout<<endl;
}

void JieMi(char fanZhiHuan[])
{
 string MiWen;  //保存密文
 cout<<endl<<"请输入密文：";
 getline(in,MiWen); //读入密文
 cout<<MiWen<<endl;
 cout<<"解密后的明文为："<<endl;
 for(int i=0; i<MiWen.length(); i++) //直接利用反置换表输出明文
 {
 if(MiWen[i]>='A' && MiWen[i]<='Z')
 cout<<fanZhiHuan[ MiWen[i] ];
 else cout<<MiWen[i];
 }
 cout<<endl;
}

void setZhiHuan(char ZhiHuanBiao[],char fanZhiHuanBiao[])
{
 int i;  //i和j是循环变量，除此之外没有任何意义
 char j;
 string s;  //密钥
 cout<<"请输入密钥（大写）："; 
 getline(in,s); //读入密钥
 cout<<s<<endl; //输出密钥
 cout<<"置换表为："<<endl;
 string s1;    
 for(i = 0 ; i < s.length();i++) //对密钥进行处理（去掉空格和重复的字符）
 {
 bool sign =0;  //标志变量
 if(s[i] >= 'A' && s[i] <='Z')
 {
 for(int j = 0; j < s1.length();j++)
 {
 if(s[i] == s1[j])
 {
  sign = 1;
  break;
 }
 }
 if(sign == 0) s1 = s1 + s[i];
 else sign = 0;
 }
 }
 for( j ='a';j<='z';j++)cout<<j<<" ";cout<<endl; //输出小写字母 从a到z 
 char ch='A';
 for( i = 'a' ;i <= 'z'; i++) //该循环利用密钥得到置换表
 {
 if(i < 'a' + s1.length()) //前面直接用s1代替
 { 
 ZhiHuanBiao[i] = s1[i-'a'];  
 }
 else //后面将剩下的"贴"上去
 {
 
 for(int j = 'a'; j < 'a' + s1.length(); j++)
 {
 if(ch == ZhiHuanBiao[j])
 {
  ch++;
  j= 'a'; //每次都从头开始搜索
  continue;
 }
 }
 ZhiHuanBiao[i] = ch;
  ch++;
 }
 cout<<ZhiHuanBiao[i]<<" "; //同时输出置换表
 }
 cout<<endl;
 for( i='a'; i<= 'z'; i++) //该循环利用置换表得到反置换表
 {
 fanZhiHuanBiao[ ZhiHuanBiao[i] ] = i;
 }
 for( i='A'; i<= 'Z'; i++) //输出反置换表
 {
 cout<< fanZhiHuanBiao[i] <<" ";
 }
 cout<<endl;
}