caesar.cpp

一个解密程序源代码

// Caesar.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <stdio.h>

int _tmain(int argc, _TCHAR* argv[])
{
//	明文是abcdefg hijklmn opqrst uvwxyz
//  密文是DEFGHIJ KLMNOPQ RSTUVW XYZABC 
	char m[80]="abcdefg hijklmn opqrst uvwxyz" ,c[80]= {0};
	 int t1[80],t2[80],i;
	 gets (m);//加密
	 for (i=0;m[i]!='\0';i++)
	   {
		 if (m[i]>='A' && m[i]<='Z')
			t1[i]=m[i]-65;
		 else if (m[i]>='a'&&m[i]<='z')
			   t1[i]=m[i]-97;
			  
		 else
			   t1[i]=-1;

	     if (t1[i] != -1)
			t2[i]=(t1[i]+3)%26;
		 else
			t2[i]=-1;
		 if (t2[i]!=-1)
		    c[i]=t2[i]+65;
		 else
		    c[i]= m[i] ;
		}
	 printf ("%s\n",c);
	 memcpy(m , c , 80) ;
	 
     //解密
	 for (i=0;m[i]!='\0';i++)
	   {
		 if (m[i]>='A'&&m[i]<='Z')
			t1[i]=m[i]-65;
		 else if (m[i]>='a'&&m[i]<='z')
			   t1[i]=m[i]-97;
			  else
				  t1[i]=-1;
			  if (t1[i]!=-1)
				 t2[i]=(t1[i]+23)%26;
			  else
				 t2[i]=-1;
			  if (t2[i]!=-1)
				 c[i]=t2[i]+97;
			  else
				  c[i]= m[i] ;
		}
	 printf ("%s\n",c);
    gets(m) ;
	return 0;
}