#include <stdio.h>
#include <conio.h>
#include <ctype.h>

void entryData();

void decodeFile();
int indexPosition(char);
char getEncodeChar(int);
char getDecodeChar(int);
void getWriteFileName(char *str);
void getReadFileName(char *str);

  char alpha[26] = "abcdefghijklmnopqrstuvwxyz";
  char filename[14];
  char readname[14];
  int option;
  FILE *fp;

  void main()
  {
    clrscr();
    printf("\nSelect any of the option from below.");
    printf("\n1. Create Encode File");
    printf("\n2. Reade Encode File\n");

    scanf("%d", &option);
    fflush(NULL);

      if( option == 1)
     getWriteFileName(filename);
      elseif( option == 2)
      {     getReadFileName(readname);
     decodeFile();
      }

    getch();
  }

   void entryData()
   {
       char chr;
       char prevchr;
       int index=-1;
       prevchr = chr;
       printf("\n Just type '::' to terminate typing. Start typing\n");
       fflush(NULL);

       while(1)
       {
       scanf("%c", &chr);
       chr = tolower(chr);

       if( chr == ':')
          if( prevchr == chr)
         break;

       if( isalpha(chr) )
       {
          index = indexPosition(chr);
          chr = getEncodeChar(index);
       }

       putc(chr, fp);
       prevchr = chr;
       }
   }

   void getWriteFileName(char *str)
   {
     printf("Enter Output File name maxium 14 character : ");
     scanf("%s", str);

     if( ( fp = fopen(str, "wt") ) == NULL  )
     {  fclose(fp);
    printf("\nInvalid file name entered.");
     }
     else
    entryData();
   }

   void getReadFileName(char *str)
   {
     printf("Enter Input File name maxium 14 character : ");
     scanf("%s", str);

     if( ( fp = fopen(str, "r+t") ) == NULL  )
     {  fclose(fp);
    printf("\nInvalid file name entered.");
     }
   }

   void decodeFile()
   {   char rchar;
       int index=-1;
       while( feof(fp) == 0 )
       {
       rchar = getc(fp);
       if( isalpha(rchar) )
       {
         index = indexPosition(rchar);
         rchar = getDecodeChar(index);
      }
      printf("%c", rchar);

       }
   }

   char getEncodeChar(int index)
   {
      int tmp=0;
      tmp = index + 5;
      if ( tmp > 25)
    tmp = tmp - 26;

      return alpha[tmp];
   }

   char getDecodeChar(int index)
   {
      int tmp=0;
      tmp = index - 5;
      if ( tmp < 0)
    tmp = 26 + tmp;

      return alpha[tmp];
   }

   int indexPosition(char chr)
   {
      int count=0;
      for( ; count < 26; count++)
      {
     if ( alpha[count] == chr)
       break;
      }
      return count;
   }

   /*******************Input*******************************
    Select any of the option from below.
    1. Create Encode File
    2. Reade Encode File

    1
    Enter Output File name maxium 14 character : output.txt

    contain of output.txt is
    ymnx nx jcfruqj tk knqj jshtinsl.
    :

    2 Read Encoded File
   ******************* OutPut*******************************
    Enter Input File name maxium 14 character : output.txt

    this is example of file encoding.
    :
   */