#include<stdio.h>

#include

#include<stdlib.h>

#include <string.h>

#define N 100

using namespace std;

//凯撒密码

//加密公式 f(a)=(a+3) mod 26

//解密公式 f(a)=(a+23) mod 26

void Encry(char *strI,int numB,int model);//加密公式函数

void Decry(char *strI,int numB,int model);//解密公式函数

int FileOut(char *strI);

int main()

{

char str[N];

     int model;

     int numB;

    

     while(1)

     {

               cout<<"凯撒密码：请选择模式:\n";

               cout<<"1.加密\n";

               cout<<"2.解密\n";

               cout<<"3.退出\n";

               cin>>model;

               cout<<endl;

              

               switch(model)

               {

                        case 1:

                              cout<<"请输入要加密的字符串:";

                                 cin>>str;

                                 cout<<"请输入该密码算法的偏移数量：";

                                 cin>>numB;

                                 Encry(str,numB,model);

                                 cout<<endl;

                        break;

                      case 2:

                              cout<<"请输入要解密的字符串:";

                              cin>>str;

                              cout<<"请输入原密码算法的偏移数量：";

                              cin>>numB;

                                 Decry(str,numB,model);

                              cout<<endl;

                     break;

                     case 3:

                              return 0;

                     break;

                      default:

                              break;

               }

     }

    

     return 0;

}

void Encry(char *strI,int numB,int model)

{//明文串 秘钥 功能模式

if(model==1)

     {

               for(int i=0; i<strlen(strI); i++)

    {

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

        {

            strI[i] = ((strI[i]-'A')+numB)%26+'A';

        }

        else if(strI[i] >= 'a' && strI[i] <= 'z')

        {

            strI[i] = ((strI[i]-'a')+numB)%26+'a';

        }

    }

    cout<<"加密完成："<<strI<<endl;

               FileOut(strI);

               cout<<"已输出到文件！"<<endl;

     }

     else

     {

               cout<<"该模式不支持此项功能！"<<endl;

     }

}

void Decry(char *strI,int numB,int model)

{

if(model==2)

     {

               int num;

               num=26-numB;

               for(int i=0; i<strlen(strI); i++)

    {

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

        {

            strI[i] = ((strI[i]-'A')+num)%26+'A';

        }

        else if(strI[i] >= 'a' && strI[i] <= 'z')

        {

            strI[i] = ((strI[i]-'a')+num)%26+'a';

        }

    }

    cout<<"解密完成："<<strI<<endl;

     }

     else

     {

               cout<<"该模式不支持此项功能！"<<endl;

     }

}

int FileOut(char *strI)

{

FILE *fp = NULL;

     int iWrite=0;

     int len=strlen(strI);



     if( strI == NULL || len ==0 )

               return false;



     //! 打开文件句柄

     if( (fp = fopen( "密文.txt","w" )) == NULL )      // 文本模式写

               return false;



     iWrite = fwrite(strI, 1, len, fp );

     fclose(fp);



     if( iWrite>0 )

               return true;

     else

               return false;

}