I have to make an LED with an ultrasonic distance sensor, the idea is to make the LED blink faster when getting closer to at an specific distance
I would say the way to go is using non-blocking code with millis(). Look into the BlinkWithoutDelay example, that comes with the Arduino IDE. It doesn't use delay(), which is considered bad coding practice, since it is just busy waiting. Nothing else can happen during a delay, except for interrupts. Instead of waiting it is better to regularily check the clock, if it is time to do something (much like you would do in real life for example for baking a pizza).

The clock is provided by millis(), which returns the number of milliseconds since startup. Below you see the BlinkWithoutDelayexample. The variable interval controls the blink frequency. If you remove the const keyword before it and change it according to the measurements from the ultrasonic sensor, you will get a changing blinking frequency with changing distance.

Try to combine the codes into one. Remove all delay() calls, except for the delay(1) (it is needed to trigger the ultrasonic sensor and it is small enough to not matter greatly).

const int ledPin =  LED_BUILTIN;// the number of the LED pin

// Variables will change:
int ledState = LOW;             // ledState used to set the LED

// Generally, you should use "unsigned long" for variables that hold time
// The value will quickly become too large for an int to store
unsigned long previousMillis = 0;        // will store last time LED was updated

// constants won't change:
const long interval = 1000;           // interval at which to blink (milliseconds)

void setup() {
  // set the digital pin as output:
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // here is where you'd put code that needs to be running all the time.

  // check to see if it's time to blink the LED; that is, if the difference
  // between the current time and last time you blinked the LED is bigger than
  // the interval at which you want to blink the LED.
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis &gt;= interval) {
    // save the last time you blinked the LED
    previousMillis = currentMillis;

    // if the LED is off turn it on and vice-versa:
    if (ledState == LOW) {
      ledState = HIGH;
    } else {
      ledState = LOW;
    }

    // set the LED with the ledState of the variable:
    digitalWrite(ledPin, ledState);
  }
}


The rest is up to you. If you need more information about the BlinkWithoutDelay example, you should google it. There are tons of tutorials. This is a great coding excerise, so have fun :)