#include <iostream>
#include "string.h"
using namespace std;

char* CaesarEncrypt(char* plaintext);
char* CaesarDecrypt(char* ciphertext);
char a[26]={'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
char b[26]={'X','N','Y','A','H','P','O','G','Z','Q','W','B','T','S','F','L','R','C','V','M','U','E','K','J','D','I'};


int main()
{
	char plaintext[105];
	printf("please input a string:\n");
	gets(plaintext);
	char *ciphertext1=CaesarEncrypt(plaintext);
	CaesarDecrypt(ciphertext1);
	getchar();
	getchar();
	return 0;
}


char* CaesarEncrypt(char plaintext[]){
	char ciphertext[105];
	int i=0;

	int sizeofplaintext=strlen(plaintext);
	for(i=0;i<sizeofplaintext;i++){
		int flag=0;
		for(int j=0;j<26;j++){
			if(plaintext[i]==a[j]){
				ciphertext[i]=b[j];
				flag=1;
			}
		}
		if(flag!=1){
			ciphertext[i]=' ';
		}
	}
	ciphertext[i]='\0';
	printf("the ciphertext is:" );
	printf("%s",ciphertext);
	char *str = new char[strlen(ciphertext) + 1];		 //分配儲存空間  
	strcpy_s(str, strlen(ciphertext) + 1,ciphertext);	 //將s中字串複製到str，最後一個空間為'\0'結束符  
	return str;
}

char* CaesarDecrypt(char* ciphertext){
	int sizeofciphertext=strlen(ciphertext);
	int i;
	char plaintext[105];
	for(i=0;i<sizeofciphertext;i++){
		int flag=0;
		for(int j=0;j<26;j++){
			if(ciphertext[i]==b[j]){
				plaintext[i]=a[j];
				flag=1;
			}
		}
		if(flag!=1){
			plaintext[i]=' ';
		}
	}
	plaintext[i]='\0';
	cout<<"\nthe plaintext is:"<<plaintext<<endl;
	return plaintext;
}