-- .-. .-- .- - ... --- -. -.-. --- -- . .... . .-. .

morse.c

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <ctype.h>

void printEncoded(char[]);
void printDecoded(char[]);

int main(int argc, char *argv[])
{
  const int BUF_LEN = 1024;
  char inputLine[BUF_LEN];

  char op;
  do {
    printf("Choose operation - [e]ncode or [d]ecode: ");
    scanf(" %c", &op);
  } while (op != 'e' && op != 'd');
  printf("Type ctrl-C or ctrl-D to quit.\n");

  while (fgets(inputLine, BUF_LEN, stdin) != NULL) {

    if (inputLine[strlen(inputLine)-1] == '\n')
      inputLine[strlen(inputLine)-1] = '\0';

    if (op == 'e')
      printEncoded(inputLine);
    else
      printDecoded(inputLine);
  }

  return 0;
}

const char UNENCODED[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ 1234567890";
const char *ENCODED[] = {
  ".-",    // A
  "-...",  // B
  "-.-.",  // C
  "-..",
  ".",
  "..-.",
  "--.",
  "....",
  "..",
  ".---",
  "-.-",
  ".-..",
  "--",
  "-.",
  "---",
  ".--.",
  "--.-",
  ".-.",
  "...",
  "-",
  "..-",
  "...-",
  ".--",
  "-..-",
  "-.--",
  "--..",  // Z
  "  ",
  ".----",
  "..---",
  "...--",
  "....-",
  ".....",
  "-....",
  "--...",
  "---..",
  "----.",
  "-----"
};  // should be same length as UNENCODED

void printEncoded(char inputLine[]) {
  for (int i=0; i<strlen(inputLine); i++) {
    for (int j=0; j<strlen(UNENCODED); j++) {
      if (toupper(inputLine[i]) == UNENCODED[j]) {
        printf("%s ", ENCODED[j]);
      }
    }
  }
  printf("\n");
}

void printDecoded(char inputLine[]) {
  char encodedChunk[6];
  int chunkIndex = 0;
  for (int i = 0; i < strlen(inputLine); i++) {
    if (inputLine[i] != ' ') {
      encodedChunk[chunkIndex++] = inputLine[i];
    }
    // when we have a space or the end of the string
    if (inputLine[i] == ' ' || i == strlen(inputLine)-1) {
      if (inputLine[i] == ' ' && inputLine[i-1] == ' ') { // it's an encoded space character
        printf(" "); // so print a space
        while (inputLine[i+1] == ' ') // and progress up to the next non-space char
          i++;
      }
      else {  // just decode the last chunk and print
        encodedChunk[chunkIndex] = '\0';
        for (int i=0; i<strlen(UNENCODED); i++) {
          if (strcmp(encodedChunk, ENCODED[i]) == 0) {
            printf("%c", UNENCODED[i]);
            break;
          }
        }
        chunkIndex = 0;
      }
    }
  }
  printf("\n");
}