Arduino get random number

Use randomSeed() Function to read an unused pin ,

  randomSeed(analogRead(A0));  // Use an unused pin 

Use random() Function to generate a random number , return long type
random() Functions can be used in two ways

random(max);     // Return number type will not   Exceed the filled data 
random(min,max); // Generate a range of random numbers 

Examples of use

void setup() {
    
  Serial.begin(9600);
  randomSeed(analogRead(A0));  // Use an unused pin 
  Serial.println(random(100)); 
  Serial.println(random(100,300));       
}

void loop(){
    

}