C++ Functionality

Hi December2000,

in addition I would suggest to implement a better kind of mapping to improve performance of toMorse. You could add a map which maps a string to a single character so you don't need to iterate through the regular array for every passed character.

You could do it somehow like this (untested) sample:

#include <map>
...
std::map< char, std::string > morseMap;
void InitMap()
{
 for ( int i = 0; i < NUM_CHARS; i++ )
 {
  morseMap[regular[i]] = morse[i];
 }
}
...
int main()
{
 InitMap();
 ...
}
...
string toMorse(char ch)
{
 std::map< char, std::string >::iterator it = morseMap.find( ch );
 if ( it == morseMap.end() )
 {
  return "UNDEFINED";
 }
 return it->second;
}

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Hope that helps,

ZOPPO

Hey Zoppo. I'm just thinking, given the universe size of an array based on a char is going to be  <=255 doesn't a vector (or string, as used here) make more sense? The look up for a vector will have a O(1) time complexity vs. the O(log n) of a map. Just an observation.

Yes, I agree, using an array/vector would be even faster if the character to search for is equal to the array entry's index ... IMO that's a good idea.

Thanks @Zoppo and  @evilrix, What is an example of how I would use array/vector?

Hm - starting from the original code you could do it somehow like this:

std::string arr[255];

void Init()
{
 for ( int i = 0; i < NUM_CHARS; i++ )
 {
  arr[regalar[i]] = morse[i];
 }
}
...
string toMorse(char ch)
{
 std::string ret = arr[ch];
 if ( false != ret.empty() )
 {
  return "UNDEFINED";
 }
 return ret;
}

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ZOPPO

Hm - maybe that can produce errors, I think you should change the occurances of char to unsigned char.

How would we write the else clause to return the results, with the if clause being ( false != ret.empty() )?  It wil always default to undefined, no?

And any time the array returned an empty sting, you would know the character was invalid.

>> How would we write the else clause to return the results
Hm? There's no need for an else clause:

In case the string is empty ret.empty() returns true so we return "UNDEFINED" in the if's execution block.

If it's not empty the ret.empty() returns false so the program continues after the if's execution block.

ZOPPO

@Zoppo ----- Thank you,

When I run the modified code comes back undefined :( .... see below

#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;

// Prototypes
string toMorse(char);

// Global data. Each valid character and its equivalent
// morse code are stored in the parallel arrays.
const int NUM_CHARS = 40;
char regular[NUM_CHARS] = { ' ', ',', '.', '?', '0', '1', '2', '3', '4', '5', 
                            '6', '7', '8', '9', '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' 
                          };

string morse[NUM_CHARS] = { " ", "--..--" , ".-.-.-" , "..--.." ,
                            "-----", ".----", "..---", "...--",
                            "....-", ".....", "-....", "--...",
                            "---..", "----.", ".-", "-...",
                            "-.-.", "-..", ".", "..-.",
                            "--.", "....", "..", ".---",
                            "-.-", ".-..", "--", "-.",
                            "---", ".--.", "--.-", ".-.",
                            "...", "-", "..-", "...-",
                            ".--", "-..-", "-.--", "--.."
                          };

int main()
{
    string str;        // To hold the user's input

    // Get a word from the user.
    cout << "Enter a word and I will translate it to Morse code.\n";
    cout << "-> ";
    getline(cin, str);

    // Translate each character and display it.
    int index = 0;
    while (index < str.size())
    {
        cout << toMorse(toupper(str[index])) << endl;
        index++;
    }

	cin.get();
    return 0;
	
}

// The toMorse function accepts a char argument and
// returns a string containing the morse code
// for that character.

std::string arr[255];

void Init()
{
 for ( int i = 0; i < NUM_CHARS; i++ )
 {
  arr[regular[i]] = morse[i];
 }
}

string toMorse(char ch)
{
 std::string ret = arr[ch];
 if ( true != ret.empty() )
 {
  return "UNDEFINED";
 }
 return ret;
} 

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Thank You! I learned so much from all of you! Cool stuff... geek it!