Adjustable Countdown Timer

#include <math.h>

int digit_pin[] = {6, 9, 10, 11}; // PWM Display digit pins from left to right

int speakerPin = 15;

#define DIGIT_ON  LOW
#define DIGIT_OFF  HIGH

int segA = 2; 
int segB = 3; 
int segC = 4; 
int segD = 5; 
int segE = A0; //pin 6 is used bij display 1 for its pwm function
int segF = 7; 
int segG = 8; 
//int segPD = ; 


int button1=13;
int button2=12;
int button3=16;
int button4=17;

int countdown_time = 60;

struct struct_digits {
    int digit[4];
  };


void setup() {                
  pinMode(segA, OUTPUT);
  pinMode(segB, OUTPUT);
  pinMode(segC, OUTPUT);
  pinMode(segD, OUTPUT);
  pinMode(segE, OUTPUT);
  pinMode(segF, OUTPUT);
  pinMode(segG, OUTPUT);

  for (int i=0; i<4; i++) {
    pinMode(digit_pin[i], OUTPUT);
  }

  pinMode(speakerPin, OUTPUT);

  pinMode(button1,INPUT_PULLUP);
  pinMode(button2,INPUT_PULLUP);
  pinMode(button3,INPUT_PULLUP);
  pinMode(button4,INPUT_PULLUP);
}


void playTone(int tone, int duration) {
  for (long k = 0; k < duration * 1000L; k += tone * 2) {  
    digitalWrite(speakerPin, HIGH);
    delayMicroseconds(tone);
    digitalWrite(speakerPin, LOW);
    delayMicroseconds(tone);
  }
}


void lightNumber(int numberToDisplay) {

#define SEGMENT_ON  HIGH
#define SEGMENT_OFF LOW

  switch (numberToDisplay){

  case 0:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_ON);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_OFF);
    break;

  case 1:
    digitalWrite(segA, SEGMENT_OFF);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_OFF);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_OFF);
    digitalWrite(segG, SEGMENT_OFF);
    break;

  case 2:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_OFF);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_ON);
    digitalWrite(segF, SEGMENT_OFF);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 3:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_OFF);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 4:
    digitalWrite(segA, SEGMENT_OFF);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_OFF);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 5:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_OFF);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 6:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_OFF);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_ON);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 7:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_OFF);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_OFF);
    digitalWrite(segG, SEGMENT_OFF);
    break;

  case 8:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_ON);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 9:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 10:
    digitalWrite(segA, SEGMENT_OFF);
    digitalWrite(segB, SEGMENT_OFF);
    digitalWrite(segC, SEGMENT_OFF);
    digitalWrite(segD, SEGMENT_OFF);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_OFF);
    digitalWrite(segG, SEGMENT_OFF);
    break;  
  }
 
}



void SwitchDigit(int digit) {
  for (int i=0; i<4; i++) {
    if (i == digit) {
      digitalWrite(digit_pin[i], DIGIT_ON);
    } else {
      digitalWrite(digit_pin[i], DIGIT_OFF);
    }
  }
}


struct struct_digits IntToDigits(int n){
  struct struct_digits dig;
  int zeros=0;
  int d;
  for (int i=0; i<4; i++) {
    d=n/pow(10,3-i);
    zeros += d;
    n = n - d*pow(10,3-i);
    if (zeros!=0 || i==3) {
      dig.digit[i]=d;
    } else {
      dig.digit[i]=10;
    }
  }
  return dig;
}

void PrintNumber(int n, int time) {
  struct struct_digits dig;

  dig = IntToDigits(n);
  
  for (int i=0; i<= time/20; i++) {
    if (digitalRead(button2)==LOW) {
      return;
    }
    for (int j=0; j<4; j++) {
      SwitchDigit(j);
      lightNumber(dig.digit[j]);
      delay(5);
    }
  }
}


bool Countdown(int n, int del){
  for (int q=n; q>0; q--){
    PrintNumber(q,del);
    if (digitalRead(button2)==LOW) {
      return false;
    }
  }
  PrintNumber(0,0);
  playTone(1519,1000);
  return true;
}



void reset() {
  int m, zeros, d, pressed3 = 0, pressed4 = 0;
  m=countdown_time;
  struct struct_digits dig;

  dig = IntToDigits(countdown_time);
  
  while (digitalRead(button1)==HIGH) {
    for (int j=0; j<4; j++) {
      SwitchDigit(j);
      lightNumber(dig.digit[j]);
      delay(5);
    }
    if (digitalRead(button3)==LOW) { 
      if (pressed3 == 0 || pressed3 > 30) {
        if (countdown_time > 0) {
          countdown_time -= 1 ;
        }
        dig = IntToDigits(countdown_time);
      } 
      pressed3 += 1;
    }
    else if (digitalRead(button4)==LOW) { 
      if (pressed4 == 0 || pressed4 > 30) {
        if (countdown_time <9999) {
          countdown_time += 1 ;
        }
        dig = IntToDigits(countdown_time);
      } 
      pressed4 += 1;
    }
    if (digitalRead(button3)==HIGH) {
      pressed3=0;
    }
    if (digitalRead(button4)==HIGH) {
      pressed4=0;
    }
  }
}

void loop(){
  reset();
  while (!Countdown(countdown_time,962)) {
    reset();
  }
  while (digitalRead(button2)==1){};
}