pico_led_button.c

#include "pico/stdlib.h"
#include "hardware/gpio.h"

const uint LED_PIN = 16;
const uint BUTTON_PIN = 15;

int init_pin() {
	gpio_init(LED_PIN);
	gpio_set_dir(LED_PIN, GPIO_OUT);
	gpio_init(BUTTON_PIN);
	gpio_set_dir(BUTTON_PIN, GPIO_IN);
	gpio_pull_down(BUTTON_PIN);
}

int main() {
	init_pin();

	while (true) {
		int state = gpio_get(BUTTON_PIN);
		gpio_put(LED_PIN, state);
	}
}

pico_led_button_with_interrupt.c

#include "pico/stdlib.h"
#include "hardware/gpio.h"

const uint LED_PIN = 16;
const uint BUTTON_PIN = 15;

void interrupt_handler(uint gpio, uint32_t events) {
	if (events & 0b0100)		// when the button is released
		gpio_put(LED_PIN, 0);
	else if (events & 0b1000)	// when the button is pressed
		gpio_put(LED_PIN, 1);
}

int init_pin() {
	gpio_init(LED_PIN);
	gpio_set_dir(LED_PIN, GPIO_OUT);
	gpio_init(BUTTON_PIN);
	gpio_set_dir(BUTTON_PIN, GPIO_IN);
	gpio_pull_down(BUTTON_PIN);
}

int main() {
	init_pin();

	gpio_set_irq_enabled_with_callback(BUTTON_PIN, GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL, true, interrupt_handler);

	while (true) {
		// this core can do other job now
	}
}