simpleEncode.c

/*
 *  simpleEncode.c
 *
 *  reads in a permutation of the alphabet then encodes
 *  lower case letters using that permutation
 *  module 4 template code you asked for - might need some cleaning up...
*
 *  Created by Julian Saknussemm on 11/09/1752
 *  Licensed under Creative Commons BY 3.0.
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>

#define STOP -1
#define ALPHABET_SIZE 26
#define ALPHABET "abcdefghijklmnopqrstuvwxyz"

char encode (int plainChar, char *permutation);
void testEncode (void);

int main (int argc, char *argv[]) {

   testEncode();

   char permutation[ALPHABET_SIZE + 1];
   scanf ("%s", permutation);
   // getchar() reads and returns one character from the keyboard
   // returns -1 when the input is finished / end-of-file is reached
   // signal this from the kayboard by pressing ^D in linux/^Z windows
   int plainCharacter = getchar();
   while (plainCharacter != STOP) {
      int encodedCharacter = encode (plainCharacter, permutation);
      printf ("%c", encodedCharacter);
      plainCharacter = getchar();
   }
   
   return EXIT_SUCCESS;
}

void testEncode (void) {
   assert (encode ('A',"abcdefghijklmnopqrstuvwxyz") == 'A');
   assert (encode ('?',"abcdefghijklmnopqrstuvwxyz") == '?');
   assert (encode (' ',"abcdefghijklmnopqrstuvwxyz") == ' ');
   assert (encode ('\n',"abcdefghijklmnopqrstuvwxyz") == '\n');

   assert (encode ('a',"abcdefghijklmnopqrstuvwxyz") == 'a');
   assert (encode ('m',"abcdefghijklmnopqrstuvwxyz") == 'm');
   assert (encode ('z',"abcdefghijklmnopqrstuvwxyz") == 'z');

   assert (encode ('a',"bcdefghijklmnopqrstuvwxyza") == 'b');
   assert (encode ('m',"bcdefghijklmnopqrstuvwxyza") == 'n');
   assert (encode ('z',"bcdefghijklmnopqrstuvwxyza") == 'a');

   assert (encode ('a',"qwertyuiopasdfghjklzxcvbnm") == 'q');
   assert (encode ('b',"qwertyuiopasdfghjklzxcvbnm") == 'w');
   assert (encode ('z',"qwertyuiopasdfghjklzxcvbnm") == 'm');
}

char encode (int plainChar, char *permutation) {
   char *alphabet = ALPHABET;
   char encodedChar = plainChar;
   int marker = 0;
   
   while (marker < ALPHABET_SIZE) {
      if(plainChar == alphabet[marker]) {
         encodedChar = permutation[marker];
      }
      
      marker++;
   }
   
   return encodedChar;
}