#include<stdio.h>
#include<iostream>
#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;
}
