lookup table using struct

[RytisBe]

Hello, i can't print corresponding decoded character to serial, do you know where did i go wrong? Thank you in advance!

// _____________________ Header Files _____________________

#include <ee108.h>
#include <ee108_switches.h>

// _________________________ Types ________________________

struct MorseCode {
  char decodedChar; // this represents the decoded character
  const char *encodedStr; // the represents the morse encoding
};

typedef  struct MorseCode    MorseCode;

// _______________________ Constants _______________________

// lookup table to allow conversion from characters to morse codes
// and from morse codes to characters
const MorseCode MORSE_TABLE[] = {
  { 'A', ".-" },
  { 'B', "-..." },
  { 'C', "-.-." },
  { 'D', "-..", },
  { 'E', "." },
  { 'F', "..-." },
  { 'G', "--." },
  { 'H', "...." },
  { 'I', ".." },
  { 'J', ".---" },
  { 'K', "-.-" },
  { 'L', ".-.." },
  { 'M', "--" },
  { 'N', "-." },
  { 'O', "---" },
  { 'P', ".--." },
  { 'Q', "--.-" },
  { 'R', ".-." },
  { 'S', "..." },
  { 'T', "-" },
  { 'U', "..-" },
  { 'V', "...-" },
  { 'W', ".--" },
  { 'X', "-..-" },
  { 'Y', "-.--" },
  { 'Z', "--.." },
  { '0', ".----" },
  { '1', "..---" },
  { '2', "...--" },
  { '3', "....-" },
  { '4', "....." },
  { '5', "-...." },
  { '6', "--..." },
  { '7', "---.." },
  { '8', "----." },
  { '9', "-----" }
};

const int SUPERLOOP_DELAY_MS = 25;

const int MORSE_TABLE_SIZE = sizeof(MORSE_TABLE) / sizeof(MORSE_TABLE[0]);
const int BUFFER_SIZE = 11;

// ___________________ Function Declarration __________________

// ____________________________________________________________

void setup() {

  // set up serial
  Serial.begin(9600);
  Serial.println("\n\n\t________A4_SerialMorseToChar________\n");

}

void loop() {

  char buf[BUFFER_SIZE] = "";

  Serial.println("\n\tType a pattern of . and - chars & hit send:");

  int bufIndex = 0;

  // read characters & break out of while loop if end of line,
  // space character or max buffer size is detected.
  while (bufIndex < BUFFER_SIZE) {
    char symbol;

    // wait until at least one character has been entered
    while (Serial.available() == 0)
      continue;

    // OK, we now have at least 1 character
    symbol = Serial.read(); // read 1 character

    // a newline or space indicates the end of the word
    // so we'll break out to process it
    if ((symbol == '\n') || (symbol == '\r') || (symbol == isspace(symbol))) {
      if (bufIndex > 0)

        break;
    }

    // ignore any characters that are not alphabetic
    if (symbol != '.' && symbol != '-')
      continue; // go directly to next iteration of while loop

    // at this point only valid characters should be left
    buf[bufIndex] = symbol; // add the character to the buffer
    bufIndex++; // increment index

  }

  // newline, space or max number of characters?
  buf[bufIndex] = '\0'; // add nul terminator to buf

  Serial.print("\tInput was: ");
  Serial.println(buf);

  for (bufIndex = 0; bufIndex < MORSE_TABLE_SIZE; bufIndex++) {

    if (buf == MORSE_TABLE[bufIndex].encodedStr) {
      Serial.print("Decoded character is: ");
      Serial.println(MORSE_TABLE[bufIndex].decodedChar);

    }
  }
}

[dhayden]

This is nice code for a beginner. I hope you'll continue to pursue programming.

The problem is line 122 which compares the address of buf to the address of MORSE_TABLE[bufIndex].encodedStr. You want to compare the contents. For that, use strcmp(). Strcmp returns a negative number, 0, or a positive number if the first string is less than, equal to, or greater than the second, so you want:
if (strcmp(buf, MORSE_TABLE[bufIndex].encodedStr) == 0) {

Hint: because strcmp's return value is the opposite of the way we normally think, I always compare it to zero. To me, the above code is easier to understand than:
if (!strcmp(buf, MORSE_TABLE[bufIndex].encodedStr)) {

One other comment: You have a spin loop while waiting for data to be available. That will burn CPU time and power. If possible, add a short delay (maybe 0.01 seconds) before line 91.

[RytisBe]

Thank you a lot for your help!

However, what happens now is that whatever i pass in let's say ".....-.-.-.-.-" (which is also not found int lookup table) still gets executed..

  for (bufIndex = 0; bufIndex < MORSE_TABLE_SIZE; bufIndex++) {

    if (strcmp(buf, MORSE_TABLE[bufIndex].encodedStr) == 0) {
      Serial.print("\tDecoded character is: ");
      Serial.println(MORSE_TABLE[bufIndex].decodedChar);
    }
  }

[jonnin]

I am not 100% sure but
".....-.-.-.-.-"

looks like
.... H
.-. R
-.-. C (or K??)

etc which brings up an issue... I don't see how it knows which letter to pick if the first 3 are one letter and the 4th makes a different letter...?

[RytisBe]

if ((symbol == '\n') || (symbol == '\r') || (symbol == isspace(symbol))) {

Well.. the output was:


Type a pattern of . and - chars & hit send:
Input was: .....-.-.-.
Input was: -.-
Decoded character is: K


This mightn't be the best example well lets assume the input is not found on the look up table, for example if i pass in : ''..--..--''

The outcome is:

Type a pattern of . and - chars & hit send:
Input was: ..--..--

My question is why did it get executed if this particular combination of "." "-" is not in the lookup table..

[RytisBe]

I do not want to be annoying here, but if anyone has some useful advice on this I would really appreciate. This is my college work and submission is due tomorrow. Thank you, once again!

[dhayden]

Line 98 isn't checking for a space correctly. It should be:
if ((symbol == '\n') || (symbol == '\r') || isspace(symbol)) {

That may explain where here:

Input was: .....-.-.-.
Input was: -.-
Decoded character is: K

You're getting that very long line of dots and dashes (.....-,-.-.) that don't match anything.

[Thomas1965]

@dhayden

Line 98 isn't checking for a space correctly. It should be:
if ((symbol == '\n') || (symbol == '\r') || isspace(symbol)) {

\r and \n are included in isspace so if (isspace(symbol)) should do.

http://www.cplusplus.com/reference/cctype/isspace/

[RytisBe]

But my question remains the same... if it doesn't match anything in the lookup table and

if (strcmp(buf, MORSE_TABLE[bufIndex].encodedStr) == 0) {

is not equal 0, shouldn't it just do nothing?? What i want to do is Serial.print("UNKNOWN"); if it doesn't match anything. But i can't get it working..

[48T7M4Gy]

@OP This again appears to be an Arduino type exercise and if so the Arduino String type would be a better choice of Morse encoded data type than char[] which is especially cumbersome without a terminating character in the data stream.

https://www.arduino.cc/en/reference/string
https://www.arduino.cc/en/Reference/StringObject

[Thomas1965]

I see two options.

1.) Check first if you the character is valid before starting to search the table. If not print an error
msg.

2.) Write a function int GetMorseCodeIndex(char ch) that returns the index of the entry or -1 if it is not there. In main you print an error msg if it is not there.

[RytisBe]

  for (bufIndex = 0; bufIndex < MORSE_TABLE_SIZE; bufIndex++) {

    if (strcmp(buf, MORSE_TABLE[bufIndex].encodedStr) == 0) {
      Serial.print("\tDecoded character is: ");

      int i;

      for (i = 0; i < buf; i++) {
        if (buf[i] == MORSE_TABLE[bufIndex].encodedStr[i]) {
          Serial.println(MORSE_TABLE[bufIndex].decodedChar);
        }
        else
          Serial.println("not found!");
        break;
      }
    }
  }

I did this, however it never gets to else statement...
I am really stuck here.

[Thomas1965]

I was thinking about sth. like this:

int GetMorseCodeIndex(char ch)
{
   for (int i = 0; i < MORSE_TABLE_SIZE; i++)
   {
      if (MORSE_TABLE[i].decodedChar == ch)
        return i; // found it
   }
   return -1; // not found
}

INSIDE loop()

for (int i = 0; i < strlen(buf); i++) // check each char in buf
{
   int idx = GetMorseCodeIndex(buf[i]); // find index of buf[i] in table
   if (idx != -1) // found
      // use MORSE_TABLE[idx].encodedStr
   else
   {
       // handle error / invalid char
   }
}

[RytisBe]

Thank you!