Arduino interrupt example

sketch.ino

#include <stdio.h>
#include <LiquidCrystal.h>

#define BUTTON_PIN 2
#define LCD_LINE_LENGTH 17

volatile int state = 1;
static char buffer0[LCD_LINE_LENGTH];
static char buffer1[LCD_LINE_LENGTH];

LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

void lcdPrintLine(char *buffer, byte lineNumber)
{
    lcd.setCursor(0, lineNumber);
    byte i = 0;

    while (i < LCD_LINE_LENGTH && buffer[i] != '\0')
    {
        lcd.write(buffer[i]);
        i++;
    }
}

void interrupt()
{
    state = digitalRead(BUTTON_PIN);
    sprintf(buffer1, (state ? "continue..." : "interrupt!!"));
    lcdPrintLine(buffer1, 1);
}

void setup()
{
    lcd.begin(16, 2);
    pinMode(BUTTON_PIN, INPUT_PULLUP);
    attachInterrupt(0, interrupt, CHANGE);
}

void loop()
{
    lcd.clear();

    for (int i = 0; i < 25; i++) {
        while( ! state);
        sprintf(buffer0, "n = %d", i);
        lcdPrintLine(buffer0, 0);
        delay(500);
    }
}