Is there a way to implement Morse code inside an array?

Question

I'm making my microcontroller display letters of the alphabet in Morse code using LEDS (dot == short blink, dash == long blink).

I could make a switch statement and do it like this :

switch (input)
case "a | A" 
.... 
case "b | B "
....

but then I'd have a 27+ long switch statement, so I guess that's not very good?

I was thinking of making an array with all the Morse code inside but how do I implement this concept, that the first entry of the array equals a or A, ... ?

Answer 1

If we assume that your platform uses a character-encoding system in which the 26 Latin alphabet letters have consecutive values (the most common system used, ASCII, does, but it's not guaranteed by the C Standard), then we can define an array of strings for the Morse code for each letter and index into that array using the value of a given letter from which the value of 'A' has been subtracted.

We can also do a similar thing for digits (these are guaranteed by the Standard to have contiguous codes).

Here's a sample code (we convert all letters to uppercase before indexing into the Morse array):

#include <stdio.h>
#include <ctype.h>

int main()
{
    const char* Alpha[26] = {
        ".-",   // 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
    };
    const char* Digit[10] = {
        "-----",// 0
        ".----",// 1
        "..---",// 2
        "...--",// 3
        "....-",// 4
        ".....",// 5
        "-....",// 6
        "--...",// 7
        "---..",// 8
        "----.",// 9
    };
    char input[256];
    do {
        printf("Enter text ($ to quit): ");
        scanf("%255s", input);
        printf("Morse code...\n");
        for (char *c = input; *c; ++c) {
            if (isalpha(*c)) printf("%s", Alpha[toupper(*c) - 'A']);
            else if (isdigit(*c)) printf("%s", Digit[*c - '0']);
            else if (*c != '$') printf("<error>");
            printf("\n");
        }
    } while (input[0] != '$');
    return 0;
}

If we can not rely on contiguous codes for the letters (or choose not to, for a more robust implementation), we can determine the index by calling the strchr function (we must then #include <string.h>) to get our letter's position in a list of all letters:

    //...
    const char* Letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    //...
        if (isalpha(*c)) printf("%s", Alpha[strchr(Letters,toupper(*c)) - Letters]);

Please feel free to ask for any further clarification and/or explanation.