#include <math.h>

#define THERMISTOR 5
#define SWITCH 9
#define A_PIN 2

const int cent = 0;
const int fahr = 1;
const int abso = 2;
int units = cent;

void setup(void)
{
  for (int i = 0; i < 7; i++)
    pinMode(A_PIN + i, OUTPUT);
  pinMode(SWITCH, INPUT);
}
 
void loop(void)
{
  double rt = 1.0 / 298.15 + log(1024.0 / analogRead(THERMISTOR) - 1) / 3977.0;  
  double t = 1.0 / rt;

  if (!digitalRead(SWITCH)) {
    if (++units > abso)
      units = cent;
  }
    
  if (units != abso) {
    t -= 273.15;
    if (units == fahr)
      t = t * 9.0 / 5.0 + 32;
  }
    
  if (t < 0) {
    t = -t;
    minus();
  }

  int temp = (int)(t + 0.5);
  boolean zero = true;
  for (int pow = 100; pow > 0; pow /= 10) {
    int dig = temp / pow;
    temp -= dig * pow;
    zero = zero && (dig == 0);
    if (!zero) {
      digit(dig);
    }
  }
  
  if (units == fahr)
    fahrenheit();
  else if (units == cent)
    centigrade();
  else if (units == abso)
    absolute();
}

const int A = 1 << 0;
const int B = 1 << 1;
const int C = 1 << 2;
const int D = 1 << 3;
const int E = 1 << 4;
const int F = 1 << 5;
const int G = 1 << 6;

static int digits[] = {
  A | B | C | D | E | F,
  B | C,
  A | B | G | E | D,
  A | B | G | C | D,
  F | G | B | C,
  A | F | G | C | D,
  A | F | E | G | C | D,
  A | B | C,
  A | B | C | D | E | F | G,
  A | B | C | F | G,
};

void digit(int d) 
{
  bits(digits[d]);
}

void minus()
{
  bits(G);
}

void centigrade() 
{
  bits(A | F | E | D);
}

void fahrenheit()
{
  bits(A | F | E | G);
}

void absolute()
{
  bits(A | B | C | E | F | G);
}

void bits(int bits)
{
  int b = 1;
  for (int i = 0; i < 7; i++) {
    int pin = A_PIN + i;
    digitalWrite(pin, LOW);
    if (bits & b)
      digitalWrite(pin, HIGH);
    b *= 2;
  }
  delay(750);
}