Here I'll be adding some basic adruino basic code.

Arduino Codes

..

Blink Using Delay function

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);                       // wait for a second
  digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);                       // wait for a second
}

Blink without delay function

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
  digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
}

Fading & Blinking using Serial Monitor

int state = 0;
int fading = 15;
int brightness = 0;
int ledOut = 5;
int val;
int value;

void setup() {
  Serial.begin(9600);
  // put your setup code here, to run once:
  pinMode(ledOut, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  val = Serial.read();
  val=Serial.parseInt();
  Serial.println(val);
  //value = val;
  //value = Serial.parseInt();
  
  if(val == 1){
     digitalWrite(ledOut, HIGH);
     delay(200);
     digitalWrite(ledOut, LOW);
     delay(200);
  } 
  else{
   analogWrite(ledOut, brightness);
   brightness = brightness + fading;
  
   if(brightness <= 0 || brightness >= 255){
    fading = -fading;
   } 
   delay(30);
  }
}

Fading when push button click

int ledPin = 5;
int inPin = 13;
int val = 0;
int brightness = 0;
int fadeAmount = 5;

void setup() {
  Serial.begin(9600);
  // put your setup code here, to run once:
  pinMode(ledPin, OUTPUT);
  pinMode(inPin, INPUT);

}

void loop() {
  // put your main code here, to run repeatedly:
  val = digitalRead(inPin);
  
  if(val == HIGH)
  {
    Serial.print("Blinking");
    digitalWrite(ledPin, HIGH);
    delay(200);
    digitalWrite(ledPin, LOW);
    delay(200);
  }
  else{
    Serial.print("Fading");
    // set the brightness of pin 5:
    analogWrite(ledPin, brightness);

    // change the brightness for next time through the loop:
    brightness = brightness + fadeAmount;

    // reverse the direction of the fading at the ends of the fade:
    if (brightness <= 0 || brightness >= 255) {
      fadeAmount = -fadeAmount;
    }
    // wait for 30 milliseconds to see the dimming effect
    delay(30);
  }
}

LDR Basic Test

void setup() {
  Serial.begin(9600);
  pinMode(8,OUTPUT);
  pinMode(A0,INPUT);
  // put your setup code here, to run once:

}

void loop() {
  int value=analogRead(A0);
  Serial.println(value);
  if(value>100){
  digitalWrite(8,LOW);
}else{
  digitalWrite(8,HIGH);
}
  // put your main code here, to run repeatedly:

}

one blinking another fade LED

int ledPin = 13;                 // LED connected to digital pin 13
int fadePin = 3;
unsigned long nextBlink, nextFade;
int fadeBrightness = 0;
char ledState = LOW, fadeDir = 10;

void setup()
{
   pinMode(ledPin, OUTPUT);      // sets the digital pin as output
   pinMode(fadePin, OUTPUT);
   ledState = LOW;
   nextBlink = millis();
   nextFade = millis();
}

/*
* This checks whether it's time to change the state of the LED, and
* does the write if so.  But it doesn't execute delay(), so in either
* case it takes essentially no time to execute.
*/
void blink(void)
{
   unsigned long now;
   now = millis();
   if (now >= nextBlink) {
       nextBlink = now + 1000;    // Next change in one second
       if (ledState == LOW) {
           digitalWrite(ledPin, HIGH);
           ledState = HIGH;
       } 
       else {
           digitalWrite(ledPin, LOW);
           ledState = LOW;
       }
   }
}

void fade(void)
{
   unsigned long now;
   now = millis();
   if (now >= nextFade) {
       nextFade = now + 200;    // Next change in one second
       if (fadeDir > 0) {
           if (fadeBrightness > (255 - fadeDir)) {
               fadeDir = - fadeDir;
           }
       } 
       else {
           if (fadeBrightness < (-fadeDir)) {
               fadeDir = - fadeDir;
           }
       }
       fadeBrightness += fadeDir;
       analogWrite(fadePin, fadeBrightness);
   }
}

void loop()
{
   blink();
   fade();
}

PIR(Passive Infered) to detect motion and make the Buzzer work

int val = 0;                    // variable for reading the pin status
 
void setup() {
  pinMode(8, OUTPUT);      // declare LED as output
  pinMode(2, INPUT);     // declare sensor as input
 
  Serial.begin(9600);
}
 
void loop(){
  val = digitalRead(2);  // read input value
  
  if(val == 1){
    //pirState = HIGH;
    //Serial.print("Motion detected");
    digitalWrite(8, HIGH);
  }
  else{
   pirState = LOW;
   digitalWrite(8, LOW); 
  }
}

Showing text into LCD

#include<LiquidCrystal.h>

const int rs = 10, en = 12, rw = 11, d0 = 2, d1 = 3, d2 = 4, d3 = 5;
LiquidCrystal lcd(rs, en, rw, d0, d1, d2, d3);
int backLight = 13;
  
void setup() {
  // put your setup code here, to run once:
  pinMode(backLight, OUTPUT);
  digitalWrite(backLight, HIGH);
  lcd.begin(16, 2);
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Hello ");
  lcd.setCursor(0, 1);
  lcd.print("Wrold");
}

void loop() {
  // put your main code here, to run repeatedly:

}

Spinning fan using LM35 by the help of L293D

int tempPin = A0;   // the output pin of LM35
//int fan1 = 4;       // the pin where fan is
//int fan2 = 8;        // led pin
int temp;
int tempMin = 20;   // the temperature to start the fan
int tempMax = 50;   // the maximum temperature when fan is at 100%
//int fanSpeed;
 
void setup() {
  pinMode(fan1, OUTPUT);
  pinMode(fan2, OUTPUT);
  pinMode(tempPin, INPUT);
  analogReference(INTERNAL);
  Serial.begin(9600);
}
 
void loop() {  
   temp = readTemp();     // get the temperature
   if(temp < tempMin) {   // if temp is lower than minimum temp
       //fanSpeed = 0;      // fan is not spinning
       digitalWrite(8, LOW);  
       digitalWrite(4, HIGH);     
   }
   else{
     digitalWrite(4, LOW);
     digitalWrite(8, HIGH);
   }
   
   
   Serial.print("TEMP = ");
   Serial.print(temp);
   Serial.println("DEG C");
}
 
int readTemp() {  // get the temperature and convert it to celsius
  temp = analogRead(tempPin);
  return temp * 0.4888; 
  
}

Ultra Sonic Sensor to calculate distance

int trigPin = 9;
int echoPin = 10;

long duration;
int distance;


void setup() {
  // put your setup code here, to run once:
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  
  //sets the trigPin on high state for 10micro seconds
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  
  //reads the echoPin, returns the sound wave travel time in microseconds
  duration = pulseIn(echoPin, HIGH);
  
  //calculating the distance onthe serial monitor
  distance = duration * 0.034/2;
  Serial.print("Distance: ");
  Serial.println(distance);
}