凯撒密码简单加密界面算法

/*  凯撒密码加密  And  解密
*   功能不算完善，只能正方向加密和反方向解密
*   也可以用加密，解密互逆的方式来进行明文反方向加密。
*/
//#include <stdio.h>    //之前使用getchar()时添加的
#include <iostream.h>

void encryption(char *p_R, char *p_M, int m_k );    //加密的函数
void decipher(char *p_R, char *p_M, int m_k);       //解密的函数
void main()
{
    char R[10];
    char M[10];
    int k=0;
    int change = 0;

//  while(!change)
//  {
        cout<<"选择操作, 1 为加密, 2 为解密 :"<<endl;
        cin>>change;
        if (change==1)
        {
            cout<<"输入明文:";
            cin>>R;
            cout<<"输入K值(1~25)";
            cin>>k;

            encryption(R,M,k);
//          break;
        }else if (change==2)
        {
            cout<<"输入密文:";
            cin>>R;
            cout<<"输入K值(1~25)";
            cin>>k;

            decipher(R,M,k);
//          break;
        }
        else
        {
            cout<<"输入有错，请重新输入"<<endl;
            change = 0;
        }
//  }// end of while    输入非法后循环错误, ERROR :提示死循环

    cout<<"K is :"<<k<<endl;

    cout<<"输入的为: "<<R<<endl;
    cout<<"转换后为: "<<M<<endl;
}

//加密
void encryption(char *p_R, char *p_M, int m_k )
{

    int i=0;
    while (p_R[i])
    {
        p_M[i] = p_R[i] + m_k;

        if (p_R[i]>='a' && p_R[i]<='z' && p_M[i]>'z')
        {
            p_M[i] -= 26;
        }
        else if (p_R[i]>='A' && p_R[i]<='Z' && p_M[i]>'Z')
        {
            p_M[i] -= 26;
        }
        i++;
    }
    p_R[i] = NULL;
    p_M[i] = NULL;
}

//解密
void decipher(char *p_R, char *p_M, int m_k)
{
    int i=0;
    while (p_R[i])
    {
        p_M[i] = p_R[i] - m_k;

        if (p_R[i]>='a' && p_R[i]<='z' && p_M[i]<'a')
        {
            p_M[i] += 26;
        }
        else if (p_R[i]>='A' && p_R[i]<='Z' && p_M[i]<'A')
        {
            p_M[i] += 26;
        }
        i++;
    }
    p_R[i] = NULL;
    p_M[i] = NULL;
}