#include "stdio.h"
#include "string.h"
#include "ctype.h"
#include "stdlib.h"
#define N 50

void menu();/*顯示菜單*/
char * inputPandK();/*輸入明文和密鑰*/
void caesar();/*愷撒加密算法*/
void vigenere();/*維吉尼亞加密算法*/

int main()
{
    menu();

    system("PAUSE");
    return 0;
}

void menu()
{
    int i=0;

    printf("  Clssical encrption program: \n");
    printf("****0-----------EXIT              **** \n");
    printf("****1-----------Keasar        **** \n");
    printf("****2-----------Vigenere     **** \n");
    printf("******************************* \n");
    
    printf("Choose your option: ");
    scanf("%d",&i);
        
    switch(i)
    {
        case 0: break;
        case 1: caesar();
                      break;
        case 2: vigenere();
                     break;
        default:break;
      }
}

//輸入明文和密鑰
char* inputPandK()
{
    char * plntxt;//聲明一個明文指針類型
    int i = 0,choose = 0;
     //開辟一塊內存空間
    plntxt = (char *)malloc(N * sizeof(char));
    if(plntxt == NULL)
    {
         printf("Memory location failed!");
         exit(-1);
    }
    /*輸入明文*/
    printf("****Enter plaintext: \n");
    fflush(stdin);
    while(i < N)
    {    
        plntxt[i] = getchar();
  //如果輸入不合法，跳出循環，最后一個元素賦值為空
        if(plntxt[i] > 126 || plntxt[i] < 32) 
  {
   plntxt[i] = '\0';
            break;
  } 
  else 
            i++;
    } 
 //返回該數組首地址
    return plntxt;
}

void caesar()
{
    char* _plntxt;//明文指針
    int* _cphrtxt;//密文指針
    unsigned int i,j;
    unsigned char key = 0;
 //接收明文
    _plntxt = inputPandK();
 printf("Enter the key:");
    scanf("%c",&key);
 while(!isdigit(key))
 {
  //key = 0;
  printf("Your input is error! \n");
     printf("Enter the key again: \n");
        scanf("%c",&key);
 }

    _cphrtxt = (int *)malloc(N * sizeof(int));
    if(_cphrtxt == NULL)
    {
        printf("Memory location failed!");
        exit(-1);
    } 
    //keasar加密算法
    for(i = 0;i < strlen(_plntxt);i++)
 {   
        if(_plntxt[i] >= 'A' && _plntxt[i] <= 'Z')
   //直接轉換為小寫
            _cphrtxt[i] = (_plntxt[i]%'A' + key)%26 + 'a';
        else if(_plntxt[i] >= 'a' && _plntxt[i] <= 122)
   //直接轉換為大寫
            _cphrtxt[i] = (_plntxt[i]%'a' + key)%26 + 'A';
     else 
   //如果為其他字符，則不變輸出
            _cphrtxt[i] = _plntxt[i];
 }  
   //輸出密文
  printf("The ciphertext is :");
  for(j = 0;j <= i;j++)
   printf("%c",_cphrtxt[j]);

     free(_plntxt); 
  free(_cphrtxt);
}

void vigenere()
{
    char* _plntxt;
 int* _cphrtxt;
 char* key;
 unsigned int i = 0,j;
 //開辟密鑰，密文空間
 key = (char *)malloc(N * sizeof(char));
    if(key == NULL)
    {
        printf("Memory location failed!");
        exit(-1);
    } 

    _cphrtxt = (int *)malloc(N * sizeof(int));
    if(_cphrtxt == NULL)
    {
        printf("Memory location failed!");
        exit(-1);
    } 
    //接受明文 
 _plntxt = inputPandK();

 printf("Enter the key: \n");
 fflush(stdin);
 while(i < N)
 {
  //
  key[i%strlen(key)] = getchar();
  if(key[i%strlen(key)] > 126 || key[i%strlen(key)] < 32)
  {
   key[i%strlen(key)] = '\0';
   break;
  }
  else 
   i++;
 }

    for(i = 0;i < strlen(_plntxt);i++)
 {   //密鑰為大寫字母
  if(key[i%strlen(key)] >= 'A' && key[i%strlen(key)] <= 'Z')
  {    //明文為大寫字母
             if(_plntxt[i] >= 'A' && _plntxt[i] <= 'Z')
                 _cphrtxt[i] = (key[i%strlen(key)]-'A' + _plntxt[i]-'A')%26 + 'a';
    //明文為小寫字母
             else if(_plntxt[i] >= 'a' && _plntxt[i] <= 'z')
                 _cphrtxt[i] = (key[i%strlen(key)]-'A' + _plntxt[i]-'a')%26 + 'A';
  } 
  //密鑰為小寫
  if(key[i%strlen(key)] >= 'a' && key[i%strlen(key)] <= 'z')
  {   //明文為大寫字母 
   if(_plntxt[i] >= 'A' && _plntxt[i] <= 'Z')
                _cphrtxt[i] = (key[i%strlen(key)]-'a' + _plntxt[i]-'A')%26 + 'a';
   //明文為小寫字母
   if(_plntxt[i] >= 'a' && _plntxt[i] <= 'z')
                _cphrtxt[i] = (key[i%strlen(key)]-'a' + _plntxt[i]-'a')%26 + 'A';
  }
  //如果為其他字符，則不變輸出
     if(key[i%strlen(key)] < 'A' || ((key[i%strlen(key)] > 'Z' && key[i%strlen(key)] < 'a')) || key[i%strlen(key)] > 'z')
            _cphrtxt[i] = _plntxt[i];
 }
 //屏幕輸出密文
 printf("The ciphertext is :"); 
 for(j = 0;j <= i;j++)
     printf("%c",_cphrtxt[j]);

    free(_plntxt); 
 free(_cphrtxt);
 free(key);
}