程序代码：

#include<stdio.h>
void main()
{
    char c;
    while((c=getchar())!='\n')
    {
    if((c>='a'&&c<='z')||(c>='A'&&c<='Z'))
    {
        c=c+4;
        if(c>'Z'&&c<='Z'+4||c>'z')
            c=c-26;
    }
    printf("%c",c);
    printf("\n");
    }
}

程序代码：

// 简单的字符加密程序.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <conio.h>
#include <iomanip>
#include <cstring>

using std::cin;
using std::cout;
using std::endl;
using std::setw;


int _tmain(int argc, _TCHAR* argv[])
{
    const int MAX = 30;
    char key;
    int count = 0;
    char Str1[MAX];
    char Str2[MAX];

    for(int flag = 1;flag != 0;)
    {
        cout << "请输入密码:";
        cin >> Str1;
        cout << "加密请输入Y/y,解密请输入N/n :";
        cin >> key;
   
        if( key == 'y' || key == 'Y')
        {
            for(int T = 0;T <= strlen(Str1) - 1;T++)
            {       
                if( T % 2 == 0 )
                    Str2[T] = Str1[T + 1];
                else
                    Str2[T] = Str1[T - 1];
            }
        for( int i = strlen(Str1) - 1;i != -1;i--)
        {
            Str1[count] = Str2[i];
            count += 1;
        }
        for(int i = 0;i <= strlen(Str1) - 1; i++)
        {
            if( Str1[i] == 'A' || Str1[i] == 'a')
                Str1[i] = Str1[i] + 3;
            else
                if( Str1[i] == 'Z' || Str1[i] == 'z')
                Str1[i] = Str1[i] - 3;
            else
                Str1[i] = Str1[i] + 1;
        }
        for(int T = 0;T <= strlen(Str1) - 1;T++)
            cout << Str1[T];
        }
        else
            if( key == 'n' || key == 'N')
        {
            for(int i = 0;i <= strlen(Str1) - 1; i++)
        {
            if( Str1[i] == 'D' || Str1[i] == 'd')
                Str1[i] = Str1[i] - 3;
            else
                if( Str1[i] == 'W' || Str1[i] == 'w')
                Str1[i] = Str1[i] + 3;
            else
                Str1[i] = Str1[i] - 1;
        }
            for( int i = strlen(Str1) - 1;i != -1;i--)
        {
            Str2[count] = Str1[i];
            count += 1;
        }
            for(int T = 0;T <= strlen(Str1) - 1;T++)
            {
                if( T % 2 == 0 )
                    Str1[T] = Str2[T + 1];
                else
                    Str1[T] = Str2[T - 1];
            }
            for(int T = 0;T <= strlen(Str1) - 1;T++)
            cout << Str1[T];
            }
            cout << endl
                << "继续请输入一个非0的值..." << endl;
            cin >> flag;
            cout << endl;
            count = 0;
}
    cout << endl
         << "Press any key...";

    _getch();
    return 0;
}