Arduino beginner problems
===

I'm very new to Arduino and experimenting with examples. I have a number of problems when using the following code:

    #include <ctype.h>
    #include <Arduino.h>
    #include "Telegraph.h"
    //#include <Telegraph.h>
    
    char* LETTERS[]  =  {
      ".-", "-...", "-.-.", "-..", ".",      // A-E
      "..-.", "--.", "....", "..", ".---",   // F-J
      "-.-", ".-..", "--", "-.", "---",      // K-O
      ".--.", "--.-", ".-.", "...", "-",     // P-T
      "..-", "...-", ".--", "-..-", "-.--",  // U-Y
      "--.."                                 // Z
    };
    
    char* DIGITS[]  =  {
      "-----", ".----", "..---", "...--",     //0-3
      "....-", ".....", "-....", "--...",     //4-7
      "---..", "----."                        //8-9
    };
    
    Telegraph::Telegraph(const int outputPin, const int ditLength){
      _outputPin  =  outputPin;
      _ditLength  =  ditLength;
      _dahLength  =  dahLength;
      pinMode(_outputPin, OUTPUT);
    }
    
    void Telegraph::outputCode(const char* code){
      for(int i=0; i<strlen(code); i++){
        if( code[i]  ==  '.' )
          dit();
        else
          dah();
      }
    }
    
    void Telegraph::dit(){
      Serial.print(".");
      outputSymbol(_ditLength);
    }
    
    void Telegraph::dah(){
      Serial.print("-");
      outputSymbol(_dahLength);
    }
    
    void Telegraph::outputSymbol(const int length){
      digitalWrite(_outputPin, HIGH);
      delay(length);
      digitalWrite(_outputPin, LOW);
      delay(length);
    }
    
    void Telegraph::sendMessage(const char* message){
      for(int i=0;  i  <  strlen(message); i++){
        const char currentChar  =  toupper(message[i]);
        if( isalpha(currentChar) ){
          outputCode(LETTERS[currentChar  -  'A']);
          delay(_dahLength);
        }else if(isdigit(currentChar) ){
          outputCode(DIGITS[currentChar  -  '0']);
          delay(_dahLength);
        }else if(currentChar  =  ' '){
          Serial.print(" ");
          delay(_ditLength * 7);
        }
      }
      Serial.println();
    }

I get the following errors:

    Telegraph.cpp:6:15: error: two or more data types in declaration of ‘LETTERS’
    Telegraph.cpp: In constructor ‘Telegraph::Telegraph(int, int)’:
    Telegraph.cpp:24:18: error: ‘dahLength’ was not declared in this scope
    Telegraph.cpp: In member function ‘void Telegraph::sendMessage(const char*)’:
    Telegraph.cpp:58:18: error: ‘LETTERS’ was not declared in this scope
    Telegraph.cpp:63:30: error: assignment of read-only variable ‘currentChar’

Sorry if this question is too general but as I mentioned, I'm very new and don't entirely understand the code.