// 004.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include "iostream.h"
#include "string.h"

//移位密碼加密
void Encrypt()
{
	int n;
	int k;
	char p[100];
	cout<<"輸入循環位移的字符個數:"<<endl;
	cin>>k;
	cout<<"輸入要加密的字母個數:"<<endl;
	cin>>n;
	cout<<"輸入以小寫表示的明文字母:"<<endl;
	for(int i=0;i<n;i++)
		cin>>p[i];
	cout<<"輸出加密后以大寫字母表示的密文:"<<endl;
	for(i=0;i<n;i++)
	{
		if(p[i]+k%26<'a')              //當字母移位后ASC||碼小于'a'時,p[i]=p[i]+k%26-6.
		{
			p[i]=p[i]+k%26-6;
			cout<<p[i];
		}
		else if(p[i]+k%26>'z')         //當字母移位后ASC||碼大于'z'時,p[i]=p[i]+k%26-58.
		{
			p[i]=p[i]+k%26-58;
			cout<<p[i];
		}
		else                      //當字母移位后ASC||碼在'a'與'z'之間時,p[i]=p[i]+k%26-32.
		{
			p[i]=p[i]+k%26-32;
			cout<<p[i];
		}
	}
		cout<<endl;
		cin.get();
}
//移位密碼解密
void Decode()
{
	int n;
	int k;
	char p[100];
	cout<<"輸入循環位移的字符個數:"<<endl;
	cin>>k;
	cout<<"輸入要解密的字母個數:"<<endl;
	cin>>n;
	cout<<"輸入以大寫字母表示的密文:"<<endl;
	for(int i=0;i<n;i++)
		cin>>p[i];
	cout<<"輸出解密后以小寫字母表示的明文:"<<endl;
	for(i=0;i<n;i++)
	{
		if(p[i]+k%26<'A')               //當字母移位后ASC||碼小于'A'時,p[i]=p[i]+k%26+58.
		{
			p[i]=p[i]+k%26+58;
			cout<<p[i];
		}
		else if(p[i]+k%26>'Z')         //當字母移位后ASC||碼大于'Z'時,p[i]=p[i]+k%26+6.
		{
			p[i]=p[i]+k%26+6;
			cout<<p[i];
		}
		else                         //當字母移位后ASC||碼在'A'與'Z'之間時,p[i]=p[i]+k%26+32.
		{
			p[i]=p[i]+k%26+32;
			cout<<p[i];
		}
	}
		cout<<endl;
		cin.get();
}

void main()
{	
	int sign=1;
	int z;
	while(sign==1)
	{
		cout<<"加密----1，解密----2，退出----0 ："<<endl;
		cin>>z;
		switch(z)
		{
			case 0: sign=0;
					break;
			case 1: Encrypt();
					cin.get();
					break;
			case 2: Decode();
					cin.get();
					break;
			default: cout<<"input error!"<<endl;
		}
	}	
}