Morse code raspberry pi pico

/**
 * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include "pico/stdlib.h"
#include "hardware/pwm.h"
#include <string.h>

#ifndef PICO_DEFAULT_LED_PIN
#warning blink example requires a board with a regular LED
#else
#define LED 25
#define SND 15

#define BASE 100
//above is base speed of single . unit of morse in milliseconds

void blink_dit() {
    gpio_put(LED, 1);
    pwm_set_gpio_level(SND, 15000);
    sleep_ms(BASE);
    gpio_put(LED, 0);
    pwm_set_gpio_level(SND, 0);
    sleep_ms(BASE);
    return;
}

void blink_dat() {
    gpio_put(LED, 1);
    pwm_set_gpio_level(SND, 15000);
    sleep_ms(BASE * 3);
    gpio_put(LED, 0);
    pwm_set_gpio_level(SND, 0);
    sleep_ms(BASE);
    return;
}

void output(char *a) {
    int i = 0;
    while (a[i] != '\0') {
        if (a[i] == '.') blink_dit();
        if (a[i] == '-') blink_dat();
        if (a[i] == 'S') sleep_ms(BASE); //represents silence one base unit long, or one .
        i++;
    }
    sleep_ms(BASE * 3);
    return;
}

void morse(char *a) {
    int i = 0, j = strlen(a);
    for (i = 0; i != j; i++) {
        if (a[i] == 'A' || a[i] == 'a') output(".-");
        if (a[i] == 'B' || a[i] == 'b') output("-...");
        if (a[i] == 'C' || a[i] == 'c') output("-.-.");
        if (a[i] == 'D' || a[i] == 'd') output("-..");
        if (a[i] == 'E' || a[i] == 'e') output(".");
        if (a[i] == 'F' || a[i] == 'f') output("..-.");
        if (a[i] == 'G' || a[i] == 'g') output("--.");
        if (a[i] == 'H' || a[i] == 'h') output("....");
        if (a[i] == 'I' || a[i] == 'i') output("..");
        if (a[i] == 'J' || a[i] == 'j') output(".---");
        if (a[i] == 'K' || a[i] == 'k') output("-.-");
        if (a[i] == 'L' || a[i] == 'l') output(".-..");
        if (a[i] == 'M' || a[i] == 'm') output("--");
        if (a[i] == 'N' || a[i] == 'n') output("-.");
        if (a[i] == 'O' || a[i] == 'o') output("---");
        if (a[i] == 'P' || a[i] == 'p') output(".--.");
        if (a[i] == 'Q' || a[i] == 'q') output("--.-");
        if (a[i] == 'R' || a[i] == 'r') output(".-.");
        if (a[i] == 'S' || a[i] == 's') output("...");
        if (a[i] == 'T' || a[i] == 't') output("-");
        if (a[i] == 'U' || a[i] == 'u') output("..-");
        if (a[i] == 'V' || a[i] == 'v') output("...-");
        if (a[i] == 'W' || a[i] == 'w') output(".--");
        if (a[i] == 'X' || a[i] == 'x') output("-..-");
        if (a[i] == 'Y' || a[i] == 'y') output("-.--");
        if (a[i] == 'Z' || a[i] == 'z') output("--..");
        if (a[i] == '0') output("-----");
        if (a[i] == '1') output(".----");
        if (a[i] == '2') output("..---");
        if (a[i] == '3') output("...--");
        if (a[i] == '4') output("....-");
        if (a[i] == '5') output(".....");
        if (a[i] == '6') output("-....");
        if (a[i] == '7') output("--...");
        if (a[i] == '8') output("---..");
        if (a[i] == '9') output("----.");
        if (a[i] == '.') output(".-.-.-SSSSSSS");
        if (a[i] == '?') output("..--..SSSSSSS");
        if (a[i] == ' ') output("SSS");
    }
    return;
}

int main() {
    int i = 0;
    uint slice_snd;

    sleep_ms(5000);

    gpio_init(LED);
    gpio_init(SND);
    gpio_set_function(SND, GPIO_FUNC_PWM);
    gpio_set_dir(LED, GPIO_OUT);

    pwm_config config = pwm_get_default_config();
    slice_snd = pwm_gpio_to_slice_num(SND);
    pwm_init(slice_snd, &config, true);

    morse("HAVING FUN WITH PULSE WIDTH MODULATION");

#endif
    return 0;
}