Arduino Learing Why we use #define

GoodWriting_1_1.c

//GoodWriting 1.1 Preprocessive director -> #define
#include <stdint.h>

///*  <----- 1
//740,9
#define LED_1 7
#define LED_2 6
#define LED_3 5
#define LED_4 4
//*/
/*  <----- 2
//774,13 (13 - 9 = 4, 4/4 = 1)
uint8_t LED_1 = 7;
uint8_t LED_2 = 6;
uint8_t LED_3 = 5;
uint8_t LED_4 = 4;
//*/
/*  <----- 3
//778,17 (17-9 = 8, 8/4 = 2)
int LED_1 = 7;
int LED_2 = 6;
int LED_3 = 5;
int LED_4 = 4;
//*/
/*  <----- 4
//786,25 (25-9 = 16, 16/4 = 4)
long LED_1 = 7;
long LED_2 = 6;
long LED_3 = 5;
long LED_4 = 4;
//*/

void setup() {

  
}

void loop() 
{
  digitalWrite(LED_1,HIGH);
  digitalWrite(LED_2,HIGH);
  digitalWrite(LED_3,HIGH);
  digitalWrite(LED_4,HIGH);
}

GoodWriting_1_2.c

#include <stdint.h>

#define _DEBUG_

#define LED_1 7
#define LED_2 6
#define LED_3 5
#define LED_4 4

void setup() 
{
  
  #ifdef _DEBUG_
  Serial.begin(115200);
  Serial.println("Hello, World.");
  #endif
  
}

void loop() 
{
  static uint8_t tg = 0;
  
  if(tg == 0)
  {
    digitalWrite(LED_1,HIGH);
    digitalWrite(LED_2,HIGH);
    digitalWrite(LED_3,HIGH);
    digitalWrite(LED_4,HIGH);
    
    #ifdef _DEBUG_
    Serial.println("All LED on !");
    #endif
  }
  else
  {
    
    digitalWrite(LED_1,LOW);
    digitalWrite(LED_2,LOW);
    digitalWrite(LED_3,LOW);
    digitalWrite(LED_4,LOW);
    
    #ifdef _DEBUG_
    Serial.println("All LED off !");
    #endif
  }
  delay(1000);
}